Acute Kidney Injury in COVID-19

Authors: Marta GłowackaSara LipkaEwelina Młynarska,*Beata Franczyk, and Jacek RyszHajime Nagasu, Academic Editor

Int J Mol Sci. 2021 Aug; 22(15): 8081.Published online 2021 Jul 28. doi: 10.3390/ijms22158081 PMCID: PMC8347536PMID: 34360866

Abstract

COVID-19 is mainly considered a respiratory illness, but since SARS-CoV-2 uses the angiotensin converting enzyme 2 receptor (ACE2) to enter human cells, the kidney is also a target of the viral infection. Acute kidney injury (AKI) is the most alarming condition in COVID-19 patients. Recent studies have confirmed the direct entry of SARS-CoV-2 into the renal cells, namely podocytes and proximal tubular cells, but this is not the only pathomechanism of kidney damage. Hypovolemia, cytokine storm and collapsing glomerulopathy also play an important role. An increasing number of papers suggest a strong association between AKI development and higher mortality in COVID-19 patients, hence our interest in the matter. Although knowledge about the role of kidneys in SARS-CoV-2 infection is changing dynamically and is yet to be fully investigated, we present an insight into the possible pathomechanisms of AKI in COVID-19, its clinical features, risk factors, impact on hospitalization and possible ways for its management via renal replacement therapy.

1. Introduction

COVID-19 is an infectious disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), and it originated in Wuhan, China, in December 2019. As of 4 March 2021, approximately 84,230,049 cases have been discovered worldwide, causing an ongoing global pandemic [1]. Such a large number of confirmed cases is related to the way the virus is transmitted, which is close human-to-human contact through droplets or aerosol via coughs, sneezes or talking. Infection may also occur by touching contaminated surfaces and then touching routes of transmission such as the mouth, eyes or nose [2]. COVID-19 disease mainly affects the respiratory system, which in more severe cases is manifested by pneumonia, hypoxemia and acute respiratory distress syndrome. Although the main focus is on the pulmonary features, physicians must be aware of complications that SARS-CoV-2 infection carries to other organs, including the kidneys [3]. Acute kidney injury (AKI) is the most common kidney manifestation among patients hospitalized with COVID-19. According to KDIGO, AKI is defined as any of the following: (1) an increase in serum creatinine (SCr) by ≥0.3 mg/dL (≥26.5 μmol/L) within 48 h; or (2) an increase in SCr ≥ 1.5 times of baseline within the prior 7 days; or (3) urine volume < 0.5 mL/kg/hour for 6 h. AKI can be also staged for severity according to KDIGO: stage (1) increase in SCr to 1.5–1.9 times baseline or by ≥0.3 mg/dL; stage (2) increase SCr to 2.0–2.9 times baseline; stage (3) increase SCr to 3.0 times baseline or increase in serum creatinine to ≥4.0 mg/dL (≥353.6 mmol/L) or initiation of renal replacement therapy [4]. Moreover, AKI development is far more frequent in severe and critically ill patients and is associated with poor prognosis and higher mortality [5,6,7]. Therefore, understanding the underlying pathophysiology of kidney injury in the course of COVID-19 is crucial for early recognition of the damage and the implementation of optimal treatment.

2. Epidemiology

With 84,230,049 cases of SARS-CoV-2 infection globally, at least one third is asymptomatic [8]. Among those COVID-19 patients who experience symptoms, about 80% develop mild to moderate symptoms, while 20% of cases present with severe symptoms over the course of the disease, of whom 6% become critically ill [9]. The overall mortality rate of COVID-19 patients is around 3% but, in the critically ill group, it can reach 50% [10].

The incidence of acute kidney injury in COVID-19 varies in different case reports. Studies in China [5,10,11] have shown that AKI occurred in 5% to 29% within a median of 7–14 days after admission, whereas reports from the United States [6,12,13] have shown greater rates reaching from 37% to 57% in COVID-19 positive patients. However, the onset of AKI in the US was observed much earlier—either upon admission or within 24 h of admission. Another study from Brazil also showed a high occurrence of AKI in 56% of COVID-19 patients, of which 67% developed stage 3 AKI [14].

Fisher et al. [13] presented a comparison report between 3345 patients with COVID-19 and 1265 patients without COVID-19 during the same hospitalization period. AKI development in the COVID-19 (+) group was higher than in the COVID-19 (−) group (57% and 37%, respectively), and a significant number of patients positive for COVID-19 had stage 3 AKI compared with patients negative for COVID-19 (17.2% vs. 7.3%). Moreover, 4.9% of the patients positive for COVID-19 required renal replacement therapy (RRT) compared with 1.6% of those negative for COVID-19. Other US studies reported RRT necessity in up to 19% of patients with COVID-19, while in Brazil it was up to 47% of patients.

The results of incidence of AKI in COVID-19 patients are presented in Table 1.

Table 1

Incidence of AKI in COVID-19 patients.

All PatientsAKIStages of AKIRRT in Patients with AKI
AKI 1AKI 2AKI 3
Yang, X. [10]5215 (29%)
Pei, G. [5]33322 (6.6%)4 (18.2%)7 (31.8%)11 (50%)
Cheng, Y. [11]70136 (5.1%)13 (1.9%)9 (1.3%)14 (2%)
Chan, L. [12]39931835 (45.9%)387 (21%)199 (10.8%)491 (26.7%)347 (19%)
Hirsch, J.S. [6]54491993 (36.6%)927 (46.5%)447 (22.4%)619 (31.1%)14.3%
Fisher, M. [13]33451903 (56.9%)942 (49.5%)387 (20.3%)574 (30.2%)164 (4.9%)
Costa, R.L.D. [14]10257 (55.9%)10 (17.5%)9 (15.8%)38 (66.7%)27 (47.4%)
Ferlicot, S. [15]471 (2.2%)3 (6.4%)2 (4.3%)41 (87.2%)30 (63.8%)

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3. Mechanism of SARS-CoV-2 Cellular Kidney Infection

It is now a well-known fact that the main target of SARS-CoV-2 is the lungs; more precisely, type II pneumocytes. More and more studies published to date have proved that not only the lungs are exposed to infection, but so are the heart, liver, gastrointestinal tract, bone marrow and kidneys [3,16] Multiorgan tropism is due to the fact that SARS-CoV-2 gains access to the cells through an endogenous viral receptor angiotensin converting enzyme 2 (ACE2) [17].

In order for SARS-CoV-2 to enter the host, cells are required to bind its transmembrane spike (S) glycoprotein to cellular receptor ACE2. S consists of two subunits, each with a different function. S1 is responsible for binding to the host cell receptor, while S2 is used to fuse the viral membrane with the membrane of the infected cell [18,19]. Spike then requires proteolytic priming to be activated, which is granted by serine protease TMPRSS2. Therefore, ACE2 and TMPRSS co-expression is a key determinant for the entry of SARS-CoV-2 into host cells [20,21]. Once SARS-CoV-2 is in the cytosol of the infected cell, the translation of its RNA and virion synthesis begins. It has been proven that genomic replication and virion assembly occur within the double vesicles of the endoplasmic reticulum (ER) and the Golgi complex [22].

We can therefore conclude that susceptible kidney cells are those that express ACE2. Using RNA-Seq sequencing techniques, scientists were able to determine which kidney cell types comprised the ACE2 gene. The data show that ACE2 mRNA is mostly expressed in proximal tubular epithelial cells and podocytes [20,21]. This would concur with a report by Braun F. et al., who managed to isolate SARS-CoV-2 from epithelial cells of an autopsied kidney [23].

4. Pathophysiology

The best understood mechanism of kidney damage induced by SARS-CoV-2 is direct cellular infection. However, there are also few possible reasons for acute renal failure, such as inflammatory damage caused by cytokine storm, AKI related to acute respiratory distress syndrome (ARDS), kidney–lung crosstalk theory, hypovolemia and collapsing glomerulopathy [24,25,26].

4.1. Direct Cellular Infection

As mentioned before, SARS-CoV-2 penetrates through angiotensin converting enzyme 2. The highest concentration of ACE2 in the kidneys was proven to be located in proximal tubular epithelial cells and podocytes [20,21,27]. Therefore, the direct infection of kidney cells by SARS-CoV-2 virus is the most likely mechanism for the development of acute kidney injury. Autopsy data also speak to this mechanism of AKI because many researchers found virus-like particles in epithelial cells of kidneys [24].

4.2. Cytokine Storm and AKI Related to ARDS

The abnormal immune response associated with SARS-CoV-2 is also a likely mechanism for the development of acute renal failure. At the root of these irregularities lies the cytokine storm and leukopenia [24]. Sepsis, a hemophagocytic syndrome, can lead to a so-called “cytokine storm”, which is a cytokine release syndrome (CRS). The most crucial cytokine responsible for this pathology is IL-6 [25]. IL-6 also occurs in ARDS complications of COVID-19. AKI in CRS is on intrarenal inflammation, increased vascular permeability, volume depletion and cardiomyopathy grounds. Cardiomyopathy can cause stasis in the renal veins, resulting in renal hypotension and hypoperfusion, leading to a reduction in the glomerular filtration rate. This phenomenon is called the syndrome type 1, which is manifested by endothelial damage, pleural effusions, edema, intra-abdominal hypertension, third-space fluid loss, intravascular fluid depletion and hypotension [28]. Moreover, other complications of COVID-19, such as right and left ventricular failure, can cause AKI. The first one leads to blood stagnation in the kidneys, whereas the second one to reduced cardiac output and then to renal hypoperfusion [24]. There are five causes of AKI in ARDS: hemodynamic instability, hypoxemia/hypercapnia, acid-base dysregulation, inflammation and neurohormonal effects [25].

4.3. Lung–Kidney Crosstalk Theory

The occurrence of kidney dysfunctions in COVID-19 patients might be explained by the kidney–lung crosstalk theory. This is due to the increased concentration of cytokines in the blood, the release of which is promoted by lung injury. Elevated levels of cytokines, especially IL-6, cause an increase in alveolar capillary permeability and pulmonary hemorrhage, and may even lead to distant-end organ dysfunction as damage to vascular endothelium in the kidneys. As a consequence, it leads to secondary hypoxia of the kidney and further damage to its structures. In patients who did not have chronic kidney disease or AKI, the research has shown that most of them manifested ARDS and/or AKI after developing pneumonia, which also testifies to the presence of lung–kidney crosstalk [28].

4.4. Hypovolemia

An incorrect distribution of fluids, especially hypovolemia (a consequence of fever and tachypnea), may affect the kidneys. This condition causes renal hypoperfusion and, consequently, renal failure. Endothelial damage, loss of fluid into the third space and hypotension provoke renal hypoperfusion. Virus cells and cytokines produced by the organism destroy the endothelium, which causes edema, ascites and hydrothorax, which in turn leads to hypotension and a loss of fluids to the third space. The amount of circulating fluid is reduced and this damages the kidneys in the prerenal mechanism. [28] Many patients infected with SARS-CoV2 have gastrointestinal symptoms that greatly increase the loss of fluid and further dehydration of the patient, mainly leading to pre-renal AKI [25]. In hemodynamically unstable patients, the venous flow deteriorates. Rhabdomyolysis (a condition involving the rapid dissolution of damaged or injured skeletal muscle), metabolic acidosis (increased level of hydrogen ions in the systemic circulation, which results in a reduction in the level of serum bicarbonate) and hyperkalemia (serum or plasma potassium level greater than 5.0 mEq/L to 5.5 mEq/L) are also associated with this condition. This has a significant impact on the degradation of kidney function and, later on, on the occurrence of AKI. [28] Therefore, optimizing hemodynamic is crucial to kidneys health.

4.5. Collapsing Glomerulopathy

Collapsing glomerulopathy (CG) is a histological term for focal segmental glomerulosclerosis defined by segmental or global glomerular collapse correlated with podocyte proliferation, whose typical feature is proteinuria. CG has been associated with various factors, but the essential one is the presence of Apolipoprotein 1 (APOL1) genotype, namely alleles G1 and G2 [29]. Since the COVID-19 outbreak, there have been several case reports presenting COVID-19 patients with CG, in which authors speculated about the possible mechanisms linking it to SARS-CoV-2 infection. Kissling et al. [30] suggested direct viral toxicity on tubular cells as a pathomechanism of acute tubular necrosis in COVID-19 patients with G1 variant of APOL1 gene, based on post-mortem kidney examination. In another report, Peleg et al. [31] failed to detect viral particles in kidney tissue; thus, cytokine storm was presumed as a cause of collapsing glomerulopathy in COVID-19 patients. Both theories are possible, especially with high-risk alleles of the APOL1 gene.

5. Histopathology

Many autopsies have been carried out since the beginning of the pandemic on COVID-19 patients, especially in the search of complications the SARS-CoV-2 virus carries to the human cells. Histopathological examinations used, among others, light microscopy, electron microscopy and immunofluorescence.

COVID-19 patients with AKI rarely showed clinical symptoms. The kidneys were often atypical in macroscopic examination, sometimes enlarged. However, microscopic examination of the subjects showed acute tubular injury (ATI), tubulointerstitial injury and glomerular injury, but nevertheless mild in relation to the degree of AKI and blood creatinine concentration [15,32]. Other notable observations were: fibrosis, congestion of the glomeruli and periurethral capillaries and the presence of glomerular fibrin. In addition, changes in the kidneys included atherosclerosis, foci of ischemia, benign chronic glomerular and tubulointerstitial lesions. Moreover, microscopy revealed the presence of isometric vacuolization in the renal tubules as an important diagnostic point. These changes in COVID-19 patients confirm direct viral infection into cells as a mechanism of AKI. Moreover, they correlate with the presence of double-membrane-covered vesicles that contain vacuoles and may be an indicator of active SARS-CoV-2 infection [32,33].

Acute tubular injury (ATI) is the constant condition found in COVID-19 patients with AKI. ATI is characterized by the loss of the brush rim, degeneration of the vacuole, flattening of the lumen of the tubule, cellular inclusions as well as necrosis and detachment of the epithelium. These changes can be well observed in samples subjected to light microscopy. The presence of hemosiderin and fibrin in the renal tubules has been rarely observed [15,23,32]. However, no aggregated platelets were observed at all. Electron microscopy revealed corona-like virus-like cells in the proximal part of the renal tubules and in podocytes. Erythrocytes were present in the lumen of the periurethral vessels [23]. The footprint of interferon in capillaries in electron microscopy indicates a cytokine storm as a mechanism for kidney damage. The visible swelling of the endothelial cells is also evidence of damage to the endothelium [15]. The most frequent histological observations are presented in Table 2.

Table 2

The most common histopathological observations in COVID-19.

Morphological DataNephron SegmentsPathophysiological Mechanism
Epithelial necrosisProximal tubulesDirect viral infections, hemodynamic disorders, rhabdomyolysis
Cellular debrisLumen of tubules
MyoglobinTubulesRhabdomyolysis
Corona-like virusesPodocytes, tubulesDirect viral infections
Isometric vacuolizationTubules
Loss of brush border, flattening, damageTubulesDirect viral infections, cytokine storm
Swelling of endothelial cellsGlomerulus

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6. Clinical Features

As mentioned before, COVID-19 can be manifested as a mild or moderate infection or a severe or critical illness. Mild or moderate symptoms include cough, fever, fatigue, dyspnea and smell and taste loss. Severe COVID-19 cases additionally present with hypoxia and >50% lung infiltration on imaging. The critical course of the disease includes respiratory failure, SIRS and/or multiple organ failure [9].

Although the main feature of COVID-19 is pneumonia, we focused our research on renal dysfunction. The most frequently reported disorder of the kidney was acute kidney injury (AKI). In researched studies [5,6,11,12,13,16], the end point of AKI was defined by the “Kidney Disease: Improving Global Outcomes (KDIGO)” criteria explained above. These findings indicate that increase in serum creatinine in COVID-19 patients at admission can be a negative prognostic factor in AKI development. In addition, majority of patients who developed AKI presented with hematuria and proteinuria, although these were more frequent in severe or critically ill patients (Table 3).

Table 3

Laboratory data in AKI patients with COVID-19.

Pei, G. [5n = 35Cheng, Y. [11n = 53Chan, L. [12n = 656Hirsch, J.S. [6n = 1993Li, Z. [34n = 147
Proteinuria84%26.0%88/147 (60%)
negative4/35 (11.4%)16/53 (30.2%)168 (26.0%)31 (21%)
+24/35 (68.6%)21/53 (39.6%)206 (31.9%)39 (27%)
++/+++7/35 (20.0%)16/53 (30.2%)194 (30.0%)15 (10%)
+++78 (12.1%)3 (2%)
p0.002<0.001
Hematuria81%46.1%71/147 (48%)
negative14/35 (40.0%)25/53 (47.2%)196 (36.2%)21 (14%)
+13/35 (37.1%)16/53 (30.2%)96 (17.7%)21 (14%)
++/+++8/35 (22.9%)12/53 (22.6%)148 (27.3%)16 (11%)
+++102 (18.8%)13 (9%)
p0.007<0.001
Serum creatinine
Serum creatinine, mg/dL0.79 (0.64–0.95)1.49 ± 0.441.42 (0.95–2.25)1.23 (0.91, 1.8)0.75 (0.61–0.93)
Peak serum creatinine, mg/dL1.84 ± 1.232.23 (1.40, 4.12)
Blood urea nitrogen
Blood urea nitrogen, mg/dL12.04 (9.0–16.0)30.8 ± 19.631 (18–51)23.0 (14.75, 37.0)0.01

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+—slight; ++—average; +++—significant.

More research is needed to determine whether the occurrence of AKI affects subsequent renal function. A study with a follow-up period of 3 weeks from the onset of the infection presented no improvement in kidney functions in 89.5% of COVID-19 patients who developed AKI [5]. Another study shows that 46% of COVID-19 patients who had AKI at discharge did not recover to baseline serum creatinine levels [12]. Therefore, the assumption that AKI may lead to CKD is possible but needs further investigation.

7. Risk Factors of AKI Development

Most of the patients who experience the severe or critical course of COVID-19 have pre-existing conditions. The most common comorbidities are hypertension and other cardiovascular disorders, diabetes mellitus and obesity. They are considered to be the major risk factors for developing a more severe, if not critical, course of COVID-19 [35]. A meta-analysis by Henry and Lippi pointed out that patients with chronic kidney failure must also take precautions in exposure to SARS-CoV-2 virus, since CKD increases the risk of a severe course of the disease [36].

In our research, we focused on the variables that specifically led to AKI occurrence in COVID-19 patients. Hirsch et al. analyzed possible risk factors associated with AKI development which included older age, diabetes, hypertension, cardiovascular disease and respiratory failure, the last one being the most important factor [6]. In another study, there was an association between older age and male sex as a primary risk factors of developing AKI [13]. Thus, not only do comorbidities play a role in the incidence of AKI, but so do non-modifiable factors such as age and gender. The results of variable correlations with AKI development are presented in Table 4.

Table 4

The correlation between age, sex, comorbid conditions and AKI development.

Pei, G. [5n = 19Chan, L. [12n = 1835Hirsch, J.S. [6n = 1993Fisher, M. [13n = 1903
Age (years)64.0 ± 8.171 (61–81)69.0 (58.0, 78.0)67.1 (15.3)
Sex (%)
Men14 (73.7)1270 (63.7)1091 (57.3)
Women734 (40)812 (42.7)
Hypertension (%)9 (47.4)820 (45)1292 (64.8)
Diabetes mellitus (%)8 (42.1)568 (31)830 (41.6)569 (29.9)
Chronic kidney disease (%)339 (18)287 (15.1)
ACEI/ARB treatment history (%)4(21.1)655 (32.9)195 (10.2)
Coronary artery disease (%)289 (14.5)
Congestive heart failure (%)244 (13)208 (10.4)87 (4.6)
Liver disease (%)99 (5)42 (2.1)
Peripheral vascular disease (%)194(11)61 (3.1)
Cancer (%)133 (6.7)38 (2.0)
Obesity (%)739 (37.1)

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Furthermore, the issue of angiotensin-converting enzyme inhibitors (ACEI) and angiotensin-receptor blockers (ARB) in patients with COVID-19 infection and putative risk of AKI in COVID19 is worth addressing. The clinical use of ACEI and ARB was controversial at the beginning of the pandemic. Some researchers proposed, based on the mechanism of SARS-CoV-2 infection, that administering ACEI and ARB could aggravate the course of the disease. This speculation has been dismissed by several observational studies, as well as international societies such as The Council on Hypertension of the European Society of Cardiology. ACEI and ARB therapy should not be discontinued in the mild and/or moderate course of COVID-19 infection [37,38].

8. Impact of AKI Development on Hospitalization and Mortality Rate

In order to assess the impact of AKI development in patients with COVID-19 on the course of hospitalization and mortality rate, we have compiled the data from five different case reports and compared AKI patients with patients without AKI (Figure 1Figure 2 and Figure 3). The occurrence of AKI in COVID-19-positive patients resulted in a significantly increased number of admissions to the intensive care unit (ICU) in comparison to COVID-19 patients without AKI. In the same group of patients, the need for mechanical ventilation was also more noticeable. What stands out the most in our sheet is the fatality rate, which ranges from 33.3% up to 86.4% in COVID-19 patients with AKI in comparison to COVID-19 patients without AKI, which varies from 5.6% to 9.3%. Therefore, patients with COVID-19 who develop AKI are at significantly higher risk of severe or critical course of the disease, respiratory failure and consequent mechanical ventilation. Moreover, AKI incidence undeniably increases the mortality rate in COVID-19 patients.

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Figure 1

Intensive care unit admission in patients with AKI and no AKI [6,12,13].

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Figure 2

The need for mechanical ventilation in patients with AKI and no AKI [6,12,13,14].

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Figure 3

In-hospital death in patients with AKI and no AKI [5,6,12,13,14].

9. Clinical Handling

There is no specific treatment for AKI caused by COVID-19, and it has to be based on KDIGO and other guidelines. Prevention of AKI mainly consists of individual fluid therapies (balanced crystalloids), discontinuation or reduction in nephrotoxic drugs and, in the case of hypovolemia, the use of vasopressors. It is important to monitor kidney function with laboratory tests such as serum creatinine and urea levels.

Treatment should be systemic. We use antiviral drugs, antibiotics, corticosteroids, renin–angiotensin inhibitors, statins and anticoagulants. Drug therapy reduces the risk of developing AKI and causes a milder disease course [39].

10. Renal Replacement Therapy

Renal replacement therapy (RRT) is needed in up to 64% of critically ill COVID-19 patients who develop AKI (Table 1) [6,12,13,14,15]. It is due to abnormal concentrations of electrolytes and volume overload resistance to pharmacological treatment. The earliest studies suggested that, in hemodynamically unstable patients with COVID-19, the recommended approach was continuous RRT (CRRT) [28]. However, clinicians observed a significantly increased incidence of circuit clotting in COVID-19 patients, leading to prolonged time of treatment, as well as the unnecessary use of resources [24,40]. Therefore, we must take caution in choosing the most safe and effective strategy.

Ramirez-Sandoval, J.C. et al. [41] reported the viability and safety of prolonged intermittent renal replacement therapy (PIRRT) as a treatment option in COVID-19 patients with AKI. The use of low-molecular-weight heparin (LMWH) in systemic anticoagulation and unfractionated heparin (UFH) in regional anticoagulation was adapted and shown to reduce the incidence of the circuit clotting observed in up to 13% of ICU patients with COVID-19 infection. These findings were later confirmed in a report by Di Mario, F. et al. [42], who tested the effectiveness of sustained low-efficiency dialysis (SLED), which is a modality of PIRRT. However, in this study, the applied anticoagulation was regional citrate anticoagulation (RCA) protocol, and it significantly lowered dialysis interruption by circuit clotting to 6.1%. Moreover, the advantages of RCA over systemic heparin anticoagulation protocols have been demonstrated in a comparative study by Arnold, F. et al. [43] Taking into account these reports, we can assume that SLED with RCA protocol is the safest and most efficient way of AKI management in hemodynamically unstable COVID-19 patients.

11. Conclusions

Acute kidney injury is common amongst patients with SARS-CoV-2 infection, especially critically ill ones, and is without a doubt associated with higher mortality. There are numerous possible pathomechanisms which are still being investigated, but the most probable ones are direct cellular invasion, ARDS, cytokine storm and hypovolemia. Histopathological reports showed that most COVID-19 patients with AKI presented acute tubular damage, sometimes with necrosis and collapsing glomerulopathy. The most important steps that should be taken in AKI prevention are the following: minimizing the risk of hypovolemia and monitoring serum creatinine levels in the early stages of COVID-19 infection, especially in regard to the high-risk patients at an older age with diabetes mellitus, hypertension and cardiovascular diseases. However, when, despite our best efforts, COVID-19 patients are hemodynamically unstable, the safest and most efficient way of AKI management is SLED with RCA protocol. The evidence related to COVID-19 is changing dynamically and we are still in need of more research for establishing the optimal treatment of AKI in COVID-19 infection. Furthermore, physicians must be aware that patients who recover from AKI induced by SARS-CoV-2 require monitoring of their kidneys on follow-up, as there is rising evidence showing eGFR decreases among patients with a history of COVID-19-associated AKI [44].

Author Contributions

All authors (M.G., S.L., E.M., B.F., J.R.) were involved in the preparation of this article and J.R. revised the final version. All authors have read and agreed to the published version of the manuscript.

Funding

This research received no external funding.

Informed Consent Statement

Not applicable.

Data Availability Statement

The data used in this article are sourced from materials mentioned in the References section.

Conflicts of Interest

The authors declare no conflict of interest.

Footnotes

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

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COVID-19 vaccination followed by activation of glomerular diseases: does association equal causation?

Authors: Nicholas L. Li,1P. Toby Coates,2 and Brad H. Rovin1,∗

Kidney Int. 2021 Nov; 100(5): 959–965.Published online 2021 Sep 14. doi: 10.1016/j.kint.2021.09.002 PMCID: PMC8437826PMID: 34534551

To date, >4 billion doses of the various severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccines have been administered worldwide in response to the coronavirus disease 2019 (COVID-19) pandemic. Even as widespread vaccination campaigns have contributed to declining case rates, adverse events are appearing beyond those originally reported in the clinical trials of vaccine efficacy and safety. Of particular relevance to the kidney is the increasing number of reports of de novo or reactivation of glomerular diseases (Table 1 12345678910111213141516171819202122232425). The occurrence of glomerular disease after immunization against influenza, pneumococcus, and hepatitis B has been reported in the past.262728 The reported patients developed acute onset nephrotic syndrome following vaccination, and kidney biopsies were consistent with a minimal change disease (MCD) pattern of injury. Although temporal association (median onset of 12 days) with vaccination and disease onset suggested a vaccine-related induction of immune injury, the pathophysiological mechanisms responsible have not been determined.

Table 1

Summary of reported cases of glomerular disease activation with COVID-19 vaccination

DiseaseAge, yr, median (range)% Female (n)Vaccine typeNo. of casesDe novo or flareaMaintenance immune therapyTemporal association to vaccination, dTreatmentOutcomeCOVID-IgG responseReferences
IgAN38 (13–52)58 (7 of 12)Pfizer–BioNTech, Moderna12De novo, 7 flareNo, or steroids, mycophenolic acid, calcineurin inhibitor in transplant patient1–2RASi, steroids, cyclophosphamideSpontaneous resolution, renal response to immunotherapyPositive1234567
MCD61 (22–”early 80s”)36 (4 of 11)Pfizer–BioNTech, Moderna, Astra Zeneca11De novo, 4 flareNo, or steroids, calcineurin inhibitor, rituximab1–13 (median, 7)Steroids, calcineurin inhibitorRenal response to immunotherapy in most casesPositive891011121314151617
MN68 (66–70)50 (1 of 2)Pfizer–BioNTech, Sinovac2De novo (anti-THSD7A+), 1 flare (anti-PLA2R+)No7–14RASiNRPositive18,19
AAN78 (52–81)33 (1 of 3)Moderna, Pfizer–BioNTech3De novoNo14Steroids, cyclophosphamide, plasma exchangeRenal responsePositive3,20,21
Anti-GBM60 (60–”older female”)100 (2 of 2)Moderna2De novoNo1–14Steroids, cyclophosphamide, plasma exchangeNo recoveryNR6,22
IgG4-RD660 (0 of 1)Pfizer–BioNTech1FlareRituximab14Steroids, rituximabRenal responsePositive23
LN42100 (1 of 1)Pfizer–BioNTech1FlareHydroxychloroquine7Steroids, mycophenolate mofetilPartial responsePositive24
Scleroderma renal crisis34100 (1 of 1)Pfizer–BioNTech1De novoNo1RASiResponsePositive25

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AAN, anti–neutrophil cytoplasmic antibody–associated nephritis; anti-GBM, anti–glomerular basement membrane antibody disease; COVID, coronavirus; COVID-19, coronavirus disease 2019; IgAN, IgA nephropathy; IgG4-RD, IgG4-related disease; LN, lupus nephritis; MCD, minimal change disease; MN, membranous nephropathy; NR, not reported; PLA2R, phospholipase A2 receptor; RASi, renin-angiotensin system inhibitor; THSD7a, thrombospondin type-1 domain-containing 7A.aDe novo indicates disease development in a patient not known to have a prior glomerular disease; flare indicates activation of a known, but controlled, glomerular disease.

After vaccination against COVID-19, reports of exacerbation, and in some cases, new onset of glomerular diseases began arriving at Kidney International and other nephrology journals. Although the development of de novo glomerular disease is intriguing, increased patient awareness of symptoms after vaccination may have prompted medical attention, revealing a previously undiagnosed kidney disease as opposed to a de novo disease. Indeed, chronicity on the kidney biopsy may suggest the glomerular disease preceded COVID-19 vaccination. Although nearly all approved vaccine platforms have been implicated, cases have been far more common after the mRNA-based vaccines, Pfizer–BioNTech BNT162b2 and Moderna mRNA1273 (Table 1). Of course, this may simply reflect more widespread use of these mRNA vaccines. Another interesting feature of COVID-19 vaccine-associated glomerular disease (CVAGD) is that most cases appear to be either IgA nephropathy (IgAN) or MCD (Table 1). The timing of IgAN activation is generally within a day or two after receiving the second dose of BNT162b2 or mRNA1273, whereas MCD appears to occur at a median of 7 days after the first dose (Table 1). Although these associations do not prove causation, we suggest that the volume of cases of MCD and IgAN and the consistent time course of events indicate a direct role of the mRNA vaccines in these 2 glomerular diseases. Several other glomerular diseases have occurred in smaller numbers following vaccination, sometimes quickly (scleroderma renal crisis), but more often after about 2 weeks (e.g., membranous nephropathy, anti–neutrophil cytoplasmic antibody–associated vasculitis, anti–glomerular basement membrane disease, and IgG4 renal disease). Given the small number of cases of these immune-mediated glomerular diseases, and the longer time to their appearance, it is difficult to be certain that they were activated by the vaccines. Nonetheless, considering these cases in aggregate, it appears that the COVID-19 vaccines can (re)activate autoantibody-mediated kidney disease.

It is not clear how COVID-19 vaccines, and in particular the mRNA vaccines, induce MCD, IgAN, and other autoimmune kidney diseases. mRNA-based vaccine technology has been available for some time, although the SARS-CoV-2 vaccines were the first to be investigated in large-scale phase 3 randomized trials. It has been previously demonstrated that this vaccine technology promotes more potent immune responses than inactivated viral vaccines and even natural infection. A comparison of the immune responses to the COVID-19 vaccine platforms is given in Table 2 29303132333435. This ability of the mRNA vaccines to enhance virus-specific responses over and above more traditional vaccines has likely contributed to the high efficacy in preventing disease from SARS-CoV-2, as well as the viral variants that have evolved during this pandemic. BNT162b2 or mRNA1273 deliver lipid nanoparticle encapsulated mRNA encoding the full-length SARS-CoV-2 spike protein. These vaccines were found to be safe and efficacious in preventing severe COVID-19 in both clinical trial and real-world conditions, although patients with known autoimmune diseases were not included in the initial trials.36 These lipid nanoparticle–mRNA vaccines stimulate robust antigen-specific T-cell responses, including T follicular helper (Tfh) cells, and potent germinal center B-cell responses, leading to durable neutralizing antibody production.37

Table 2

Immune responses to SARS-CoV-2 vaccine platforms

VaccineExample manufacturerT-cell responsesB-cell responsesCytokine responsesReferences
LNP-mRNAPfizer–BioNTech, ModernaAntigen-specific Th1-biased CD4+ response, CD8+ IFNɣ, IL-2Prolonged S-specific germinal center B-cell responsesIFNɣ, IL-2, type I interferon via toll-like receptor-7293031
Adenovirus-DNAAstraZeneca, Janssen/Johnson & JohnsonAntigen-specific Th1-biased CD4+ response, monofunctional and cytotoxic CD8+ responseIgG1/IgG3 predominant, low IgG2/IgG4IFNɣ, TNFα, IL-2, type 1 interferon via toll-like receptor-931,32
Inactivated whole virusSinovac BiotechTh1-biased response with minimal Th2RBD-specific binding antibody and neutralizing antibody productionIFNɣ, TNFα, IL-233,34
Recombinant protein subunitNovavaxTh1-biased response with minimal Th2S-binding antibody and neutralizing antibody productionIFNɣ, TNFα, IL-235

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IFNγ, interferon gamma; IL-2, interleukin 2; LNP, lipid nanoparticle; RBD, receptor-binding domain; SARS-CoV-2, severe acute respiratory syndrome coronavirus 2; Th1, T-helper cell 1; Th2, T-helper cell 2; TNFα, tumor necrosis factor alpha.

In the cases of IgAN, disease symptoms occurred right after vaccination, suggesting a rapid immune mechanism, such as a memory recall response or mobilization of cells positioned to secrete galactose-deficient IgA1 antibodies. Although purely speculative, we wonder if the COVID-19 vaccines can robustly stimulate the gut-associated lymphoid tissue (Peyer patches) responsible for IgA1 production, as they do in other lymphoid tissues. IgA1 hyperresponsiveness has been observed in patients with IgAN following influenza vaccination.38 In the case of COVID-19 vaccination, circulating IgA responses following administration have been observed to be similar in kinetics to IgG responses, with levels reaching a plateau 18 to 21 days after first mRNA dose, and further increases after a second dose peaking at 7 days after dose.39 The temporal associations with hematuria onset following vaccination on the order of days argues against the contribution of spike protein-specific IgA molecules from participating in disease. However, it is known that patients with IgAN have increased circulating galactose-deficient IgA1, and perhaps bystander activation of the immune system with mRNA COVID-19 vaccination may act as a trigger for the formation of immune complexes and subsequent glomerular injury.

In contrast, the development of MCD following vaccination takes some time, suggesting a role for cellular immunity. Central to the pathogenesis of MCD is the development of podocyte injury due to dysregulated T-cell activation.29 The COVID-19 mRNA vaccines trigger enhanced Tfh responses that peak 7 days after immunization. A potential contribution to the pathogenesis of MCD by Tfh cells has been suggested by observations that circulating subsets of Tfh cells are increased in patients with MCD, and the frequency of these populations is reduced in patients who are successfully treated with steroids.40 Given these findings, and the reported onset of disease at a time point that correlates with Tfh response, perhaps mRNA vaccine-induced alterations in the Tfh population and/or their associated cytokine profile in a susceptible individual could promote podocyte injury and the development of nephrotic syndrome and MCD.

The later appearing cases of autoantibody-mediated glomerular disease may be due to the induction of vaccine-associated autoimmunity. Vaccine-associated autoimmunity has been postulated to occur by antigen-specific and nonspecific mechanisms. Antigen-specific triggers for vaccine-mediated autoimmunity are thought to be secondary to molecular mimicry. That is, exposure to a non–self-antigen, such as SARS-CoV-2 spike protein, could elicit responses directed against host tissues if there was sufficient sequence homology to allow for cross-recognition. The SARS-CoV-2 spike protein shares homology with several human proteins, which may then be subject to off-target immune attack after vaccination.41 Consistent with the mimicry hypothesis, it has been suggested that homologous sequences between human alveolar surfactant-related proteins and SARS-CoV-2 spike glycoproteins contribute to host immune attack and the subsequent pulmonary pathology seen with COVID-19 infection.42 Similarly, mimicry of viral antigens with host proteins has been proposed to contribute to immune attack in the central nervous system, exacerbating neurologic complications in COVID-19.43

Antigen nonspecific mechanisms of autoimmunity with vaccination are thought to occur through bystander activation. In this model, the vaccine-stimulated immune response may trigger cellular damage and exposure of normally hidden self-antigens, which are then recognized by host immunity. Alternatively, by this model, innate immune responses may upregulate cytokine signaling and self-antigen presentation by antigen-presenting cells to potentially autoreactive T cells. Either of these mechanisms could conceivably contribute to the development of glomerular disease in response to vaccination, with perhaps different disease phenotypes resulting from each.

Interestingly, to date, there has been only one report of an exacerbation of lupus nephritis (LN) after COVID-19 vaccination, and this was with the BNT162b2 vaccine. This paucity of cases is somewhat unexpected. Tfh cells, robustly activated by mRNA-based COVID-19 vaccines, are important for autoantibody development in lupus.44 Germinal center and peripheral leukocyte cytokine profiles after vaccination are reminiscent of cytokine profiles from lupus patients, with especially high levels of interferon-α, interleukin-6, and tumor necrosis factor-α.45 In the reported case, a patient with known class V LN in remission developed nephrotic syndrome following the first vaccine injection, and kidney biopsy revealed International Society of Nephrology/Renal Pathology Society class II and V LN with an activity index of 0. Given the robust immune activation achieved with the mRNA vaccines, it is surprising that in this case immune complex deposits were limited to the subepithelial compartment and there was no development of proliferative LN. The absence of proliferative LN cases may arguably be because many patients who have lupus nephritis are maintained on long-term immunosuppression. Most patients who developed CVAGD were not on immunosuppression (Table 1). Perhaps a baseline level of immunosuppression is sufficient to blunt the immune response to mRNA vaccination and prevent autoimmune reactions. This is supported by the observation that solid organ transplant patients on various forms of immune suppression, including those typically used in lupus nephritis, such as glucocorticoids and mycophenolate mofetil, demonstrate a weaker response to 2 doses of BNT162b2 vaccination.46 However, considering the few reports of patients on immunosuppression who still developed glomerular injury after vaccination, including one kidney transplant patient, being on immunosuppression is clearly not the only factor determining who will develop kidney disease with these vaccines. Ultimately, there are likely individual patient-specific factors involved that determine whether vaccination results in immune protection or autoimmune injury.

In the published cases of CVAGD, glomerulonephritis was often managed with the usual therapeutic options for these diseases, frequently leading to a clinical response (Table 1). Although evidence is limited, we support a management strategy of CVAGD that is consistent with the conventional therapy of glomerular diseases not associated with vaccination, including the use of immunosuppression if typical indications develop. It is not unreasonable to extrapolate from the management of glomerulonephritis in general, given the presumption in CVAGD that the same disease mechanisms and pathways of vaccine-independent glomerular disease are activated by COVID-19 vaccination. However, management decisions should be tailored to individual cases given the rarity of these events.

As the worldwide COVID-19 vaccination campaign continues to accelerate, it is probable that we will continue to see CVAGD. Not all cases have been, or will be, reported, there is likely reporting bias, and the number of patients with known glomerular disease who have been vaccinated is not known, so the true incidence of CVAGD will be difficult to determine. As multiple doses of vaccines are now being offered, close observation to watch for an increase in CVAGD will be needed. However, in the context of the billions of doses of COVID-19 vaccine that have been administered, the relatively small number of cases thus far suggests a low incidence. Care providers should consider the possibility of glomerulonephritis in patients who develop gross hematuria or edema after vaccination to aid in the prompt diagnosis and management of these diseases. The possibility of CVAGD should not, however, prompt vaccine hesitancy. Most reported cases were easily managed and resolved on their own or responded to typical therapy. Also, COVID-19 infection itself has been linked to the development of immune-mediated kidney diseases.47 The benefits of COVID-19 vaccination appear to greatly outweigh the risks of glomerular disease occurrence or recurrence, and vaccination remains the best method of preventing the morbidity and mortality associated with SARS-CoV-2 infection. Therefore, we are offering vaccination to all of our patients with glomerular diseases, with the following considerations.

Patients in remission and off all immunosuppression should be followed up closely after vaccination and be told to report hematuria or swelling immediately for early intervention. For patients undergoing active immunosuppressive treatment with anti-metabolites (e.g., mycophenolate mofetil or azathioprine), cytotoxic drugs (e.g., cyclophosphamide), anti–B-cell therapies (e.g., rituximab), and costimulation blockers (e.g., abatacept), antibody response to COVID-19 vaccines is likely to be poor.48 , 49 It is probably reasonable to postpone vaccination until these intensive therapies have been tapered or completed. Timing is also important for anti-CD20 B-cell therapies as these have prolonged effects after dosing. For such patients, it is important to continue all preventative measures in place before vaccines were available, and all individuals within the patient’s “bubble” should be vaccinated to provide an additional layer of protection. Finally, it is difficult to speculate on the management of patients who develop CVAGD after the first injection of an mRNA-based vaccine. Checking SARS-CoV-2 antibody response after the first dose may provide some confidence that the patient developed an immune response and may not need the second dose, but of course this does not equate with protection against COVID-19. A change in vaccine platform could also be considered for a second dose. Alternatively, if the CVAGD was mild and readily resolved, administration of the follow-up dose could be considered.

The Immunonephrology Working Group of the European Renal Association–European Dialysis and Transplant Association recently published recommendations on the use of COVID-19 vaccines in patients with autoimmune kidney diseases and supports the vaccination of all individuals without known contraindications.50 However, these recommendations did not advise on whether vaccination with one vaccine platform was preferable to another. Despite the higher number of reports of glomerular disease activation or reactivation with mRNA COVID-19 vaccines compared with the traditional vaccines, it remains difficult to make a recommendation against the mRNA platform. As CVAGD has been seen with non-mRNA vaccines, avoiding Pfizer–BioNTech or Moderna vaccines does not completely eliminate autoimmune risk. Furthermore, the differences in efficacy between the various vaccines cannot be overlooked. Ultimately, as with all decisions in medicine, theoretical risks must be balanced against known benefits of interventions, and discussions between care providers and patients in this regard are important.Go to:

Disclosure

All the authors declared no competing interests.

See the article “A case of gross hematuria and IgA nephropathy flare-up following SARS-CoV-2 vaccination” in Kidney Int, volume 100 on page 238.See the article “Minimal change disease and acute kidney injury following the Pfizer-BioNTech COVID-19 vaccine” in Kidney Int, volume 100 on page 461.See the article “Relapse of primary membranous nephropathy after inactivated SARS-CoV-2 virus vaccination” in Kidney Int, volume 100 on page 464.See the article “Post-vaccinal minimal change disease” in Kidney Int, volume 100 on page 459.See the article “Minimal change disease following the Moderna mRNA-1273 SARS-CoV-2 vaccine” in Kidney Int, volume 100 on page 463.See the article “Histologic correlates of gross hematuria following Moderna COVID-19 vaccine in patients with IgA nephropathy” in Kidney Int, volume 100 on page 468.See the article “Anti-GBM nephritis with mesangial IgA deposits after SARS-CoV-2 mRNA vaccination” in Kidney Int, volume 100 on page 471.See the article “Relapse of minimal change disease following the AstraZeneca COVID-19 vaccine” in Kidney Int, volume 100 on page 459.See the article “Relapse of class V lupus nephritis after vaccination with COVID-19 mRNA vaccine” in Kidney Int, volume 100 on page 941.See the article “Letter regarding “Minimal change disease relapse following SARS-CoV-2 mRNA vaccine”” in Kidney Int, volume 100 on page 458.See the article “A case of membranous nephropathy following Pfizer–BioNTech mRNA vaccination against COVID-19” in Kidney Int, volume 100 on page 938.See the article “Minimal change disease relapse following SARS-CoV-2 mRNA vaccine” in Kidney Int, volume 100 on page 457.See the article “Gross hematuria following vaccination for severe acute respiratory syndrome coronavirus 2 in 2 patients with IgA nephropathy” in Kidney Int, volume 99 on page 1487.See the article “ANCA glomerulonephritis after the Moderna COVID-19 vaccination” in Kidney Int, volume 100 on page 473.See the article “Relapse of IgG4-related nephritis following mRNA COVID-19 vaccine” in Kidney Int, volume 100 on page 465.See the article “IgA nephropathy presenting as macroscopic hematuria in 2 pediatric patients after receiving the Pfizer COVID-19 vaccine” in Kidney Int, volume 100 on page 705.See the article “Gross hematuria following SARS-CoV-2 vaccination in patients with IgA nephropathy” in Kidney Int, volume 100 on page 466.See the article “Is COVID-19 vaccination unmasking glomerulonephritis?” in Kidney Int, volume 100 on page 469.See the article “De novo vasculitis after mRNA-1273 (Moderna) vaccination” in Kidney Int, volume 100 on page 474.See the article “Scleroderma renal crisis following mRNA vaccination against SARS-CoV-2” in Kidney Int, volume 100 on page 940.This article has been cited by other articles in PMC.

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