What we know so far:
A large proportion of people with COVID-19, particularly severe COVID-19, develop acute kidney injury (AKI). In this feature, we review the existing research on the links between COVID-19 and kidney health.
We review the existing evidence on the effect that severe COVID-19 has on the kidneys. Carlos Avila Gonzalez/The San Francisco Chronicle via Getty Images
All data and statistics are based on publicly available data at the time of publication. Some information may be out of date. Visit our coronavirus hub and follow our live updates page for the most recent information on the COVID-19 pandemic.
One of the most studied serious complications associated with COVID-19 is acute respiratory distress syndrome (ARDS), which develops when someone is not getting enough oxygen. ARDS can be life-threatening.
Based on recent research, about 30–40% of people hospitalized for COVID-19 develop ARDS, and close to 70% of fatal cases involve this complication.
However, as the pandemic continues, researchers are finding evidence that COVID-19 can cause a host of symptoms and lead to a number of different complications, not just ARDS. One of these is AKI, which is also known as acute renal failure.
In this Special Feature, Medical News Today explore what experts know so far about COVID-19 and AKI — including the outcome for people with both of these conditions — and what they still need to learn.
Stay informed with live updates on the current COVID-19 outbreak and visit our coronavirus hub for more advice on prevention and treatment.
COVID-19 and kidney damage
When SARS-CoV-2 infects cells, the first step is for the virus to attach to angiotensin converting enzyme 2 (ACE-2) receptors.
These receptors sit in the cellular membranes of cells lining the kidneys, lungs, gastrointestinal tract, heart, and arteries. They help moderate blood pressure by regulating levels of angiotensin, a protein that raises blood pressure by constricting blood vessels.
Some research suggests that SARS-CoV-2 may be more likely to target the kidneys than other parts of the body because ACE-2 expression is very high in the cells lining the proximal tubule. The proximal tubule is a major segment of the kidney responsible for the bulk of the reabsorption of water and nutrients from the blood.
Once SARS-CoV-2 enters kidney cells, it begins to replicate using the cell’s machinery. Cells often sustain damage during this process.
The immune system also sparks an inflammatory response once it recognizes the invading viral particles. This response can inadvertently cause further damage to healthy tissue.
AKI occurs when kidney damage is severe enough that the organ can no longer filter the blood properly. This impairment causes waste products to build up in the blood, making it harder for the kidneys to work and maintain the body’s fluid balance.
After some concerns over whether remdesivir, a drug that doctors use to treat COVID-19, may cause AKI, the European Medicines Agency (EMA) recently found no evidence of a link.
Some people with AKI may not have any symptoms at all. However, others may experience symptoms such as reduced urine output, unexplained exhaustion, and swelling around the eyes and in the ankles and legs.
In severe or untreated cases, AKI can lead to organ failure, which can result in seizures, coma, and even death.
COVID-19 and AKI
Researchers need to collect more patient data to build their understanding of the relationship between kidney damage and COVID-19. However, most research suggests that AKI is occurring more often during the current pandemic than it did during the 2003 SARS epidemic.
Studies published in February 2021 report varied rates. According to some research, 4–37% of COVID-19 cases involve the kidneys, and AKI has an incidence of 50% in hospitalized COVID-19 patients.
A recent review paper contradicts this finding, noting that an estimated 10% of people hospitalized for COVID-19 develop AKI. Several other studies report much higher rates, though. In a study from September 2020, 81% of patients admitted to the intensive care unit (ICU) for COVID-19 developed AKI.
In comparison, during the 2003 SARS epidemic, research showed that an estimated 6.7% of people with a SARS diagnosis experienced AKI. Also, doctors diagnosed AKI as a complication in 91.7% of fatal cases.
Some factors seem to increase the risk of developing AKI with COVID-19.
For instance, age appears to play a role. In a recent subgroup analysis involving people with COVID-19, AKI affected about 12% of people in the subgroup with an average age of over 60 years. Conversely, it only affected about 6% of people in the subgroup with an average age below 60 years.
People with preexisting kidney disease or other chronic diseases, such as hypertension, diabetes, heart disease, and obesity, are also more likely to develop COVID-19 and experience severe symptoms.
Treatments for kidney conditions, such as dialysis or immunosuppressants after receiving a kidney transplant, also weaken the immune system.
Dialysis is a process in which a machine filters a person’s blood because their kidneys can no longer perform this function. Doctors prescribe anti-rejection immunosuppressant medications to people who have undergone an organ transplant.
Both of these factors may contribute to a higher risk of severe COVID-19. Due to this, researchers and kidney organizations are calling on countries to start prioritizing people with preexisting kidney disease for COVID-19 vaccination.