Is Kidney Pain a Symptom of COVID-19?

Kidney pain is typically described as a feeling of discomfort in the back and sides of your upper abdomen. Pain in this region is referred to as flank pain. It’s felt in the area that’s below your ribs and above your hips and pelvis.

Typically, the pain is worse on one side of the body.

COVID-19 can damage the kidneys. However, kidney pain is typically not a symptom of kidney damage. In fact, many people with kidney damage may not even know it’s occurred.

More often, kidney pain is caused by conditions like:

• kidney infection, a bacterial infection typically caused by a UTI that’s spread up to the kidneys
• kidney stones, solid masses of calcium or uric acid crystals that can form in the kidneys
• hydronephrosis, where urine backs up into the kidney
• a cyst or tumor in the kidney
• polycystic kidney disease

A blood clot in the kidney may also cause kidney pain and COVID-19 does increase the risk of blood clots.

It’s also possible that you can have COVID-19 and feel pain in the area of your kidneys that isn’t actually coming from your kidneys. There are some case studies reporting flank pain in people with COVID-19 that’s due to the infection actually affecting the lower part of their lungs.

Many of the reports of kidney involvement in COVID-19 are of acute kidney injury (AKI). This is when your kidneys suddenly stop working as they should.

In some situations, AKI causes no symptoms and is only detected during testing for other health conditions. In this case, tests typically pick up on increased levels of protein, blood, or both in the urine.

When symptoms of AKI are present, they can include:

• reduced urine output
• swelling in the legs, ankles, or feet
• fatigue
• nausea or vomiting
• shortness of breath
• chest pain or pressure
• confusion

AKI is serious and needs to be treated in a hospital with supportive care and, in some cases, dialysis. Dialysis helps to remove waste products and extra fluids from your blood when your kidneys have stopped working properly.

A 2021 study reported 1,835 people with AKI due to COVID-19. Of these individuals, 347 (19 percent) required treatment with dialysis.

Developing AKI when you have COVID-19 is associated with a poorer outcome. Another 2021 study of people hospitalized with COVID-19 found that AKI was associated with a significantly higher risk of death.

How does COVID-19 damage the kidneys?

Researchers are still trying to determine how exactly SARS-CoV-2, the virus that causes COVID-19, damages the kidneys. It’s possible that one or a combination of the mechanisms below are at play:

• direct infection: Some cells in the kidneys express the receptor protein, ACE2, that SARS-CoV-2 needs to enter a host cell. Because of this, it’s possible that the virus could be directly infecting and killing these cells.
• immune activity: Some people with COVID-19 have high levels of cytokines, pro-inflammatory proteins made by the immune system in response to infection. High inflammation in the body may cause damage to kidney tissue.
• blood clots: COVID-19 can increase the risk of blood clots. These clots may clog small blood vessels in the kidneys. This can block blood flow and lead to kidney damage.
• low oxygen: Pneumonia due to COVID-19 can mean that less oxygen is entering your blood than usual. Low oxygen levels can cause many organs and tissues, including the kidneys, to not function properly.

It’s also possible that some drugs that are used to treat COVID-19 in people who are seriously ill, may contribute to kidney damage. Examples of these drugs include the antiviral drug remdesivir and certain antibiotics used to treat secondary bacterial infections.

Kidney problems seem to be a fairly common complication of severe COVID-19. However, the exact prevalence can vary by study.

Studies have documented AKI in 36.6 percent to 46 percent of people hospitalized with COVID-19. The prevalence of AKI in those admitted to the intensive care unit (ICU) for COVID-19 can be even higher, up to 78 percent.

A 2021 review analyzed AKI prevalence in COVID-19 and included 54 studies. The overall prevalence of AKI in people hospitalized with COVID-19 was 28 percent, rising to 46 percent in the ICU.

It’s important to note that most reports of kidney damage have been in people who were hospitalized with COVID-19. However, there’s some evidence that those who do not need to be hospitalized may also experience kidney damage.

The results of a 2021 study suggest that people who weren’t hospitalized with COVID-19 are still at an increased risk of adverse kidney outcomes in the future. This suggests that COVID-19 can also impact the kidneys in less serious illness.

Summary

Research has shown that the risk of acute kidney injury (AKI) seems to be highest among those who have more serious COVID-19 illness. But, there is also evidence that COVID-19 may increase the risk of future kidney disease even in people who were not hospitalized with the illness.

A 2021 study looked at the outcome of 143 people who’d been hospitalized with COVID-19 and experienced new-onset kidney disease during their illness.

After a follow-up period of 4 months, researchers found that 91 percent of people recovered from their kidney disease while 9 percent did not. People in the nonrecovery group were significantly older than those in the recovery group.

However, other research has found that kidney complications due to COVID-19 can result in decreased kidney function.

A 2021 study compared people hospitalized with COVID-associated AKI to those with AKI due to another cause. This was done by assessing eGFR, a measure of the filtering ability of the kidneys, after discharge from the hospital.

After controlling for the severity of AKI and other health conditions, people with COVID-associated AKI had a greater rate of eGFR decrease than those with AKI due to other causes.

The 2021 study mentioned earlier compared kidney function in veterans who had had COVID-19 and those who had not. The risk of serious kidney events after acute illness was found to increase with the severity of COVID-19.

However, nonhospitalized participants were also found to have a higher risk of serious kidney events in the 30 days after their illness compared to people who had not developed COVID-19. This included:

• a 15 percent higher risk of a major adverse kidney event
• a 30 percent higher risk of AKI
• a 215 percent higher risk of end-stage kidney disease

These findings suggest that people who’ve had COVID-19 may need additional follow up after their illness that includes assessments of kidney function. This is particularly true for people who were hospitalized with COVID-19.

Various studies have looked into risk factors for developing AKI or other kidney issues due to COVID-19. Based on the findings of these studies, potential risk factors for kidney issues from COVID-19 may include:

• having more severe COVID-19 illness
• older age
• preexisting kidney disease, such as chronic kidney disease (CKD)
• other preexisting health conditions like diabetes, high blood pressure, or cardiovascular conditions
• Black race, potentially due to disparities in healthcare access or to socioeconomic inequalities

Kidney pain isn’t typically a symptom of COVID-19. However, it’s possible for people with COVID-19 to feel pain in the area of their kidneys that’s actually related to other areas, such as the lungs.

COVID-19 can damage the kidneys, although this doesn’t typically cause kidney pain. Most of the research into kidney damage is in hospitalized patients, but COVID-19 may also affect the kidneys of people with less severe illness.

Some people, such as those with chronic kidney disease and certain other health conditions, may be at a higher risk of COVID-related kidney issues. If you’re at a higher risk and have had COVID-19, talk to your doctor about their recommendations for follow-up tests to assess your kidney function.