Researchers have pointed to a significant decline in kidney function in Covid-19 long-haulers and even among those who had mild infections of the virus.

The study, by researchers at Washington University School of Medicine in St. Louis, showed that people infected with SARS-CoV-2 are at an increased likelihood of developing kidney damage as well as chronic and end-stage kidney diseases.

The study is published online in the Journal of the American Society of Nephrology.

Known as the silent killer, kidney dysfunction and disease tend to be free of pain and other symptoms so much so that the National Kidney Foundation estimates that 90 per cent of the people with failing kidneys don’t know it.

“Our findings emphasise the critical importance of paying attention to kidney function and disease in caring for patients who have had Covid-19,” said Ziyad Al-Aly, Assistant Professor of Medicine at Washington University.

“If kidney care isn’t an integral part of Covid-19 post-acute care strategy, then we will miss opportunities to help potentially hundreds of thousands of people who have no idea that their kidney function has declined due to this virus,” Al-Aly added.

The researchers created a controlled dataset that included health information from more than 1.7 million healthy and Covid-infected older adults from March 1, 2020, through March 15, 2021.

The team also analysed data that included 1,51,289 women — including 8,817 with Covid-19 — and adults of all ages.

“The risk of decreased kidney function is highest among the people who were in the ICU; however, it’s important to note that the risk extends to all patients, even those who had milder cases of Covid-19,” said Al-Aly.

Further, people who had mild disease, but did not need to be hospitalisation had a 15 per cent higher risk of suffering from a major adverse kidney event such as chronic kidney disease, a 30 per cent higher risk of developing acute kidney injury, and a 215 per cent (more than two-fold) higher risk of acquiring end-stage kidney disease.

The risk increased for patients hospitalised for Covid-19, and considerably so for those who were in the ICU for the virus: seven times the risk of experiencing a major adverse kidney event, eight times the risk of acute kidney injury and 13 times the risk of end-stage kidney disease.