ROCHESTER, Minn. — As many as half of all patients hospitalized with COVID-19 leave the hospital with acute kidney injury, according to a recent study in the journal JAMA Network Open, with the decline following discharge coming on quicker and lasting longer, independent of whether you have kidney disease prior to hospitalization.

Previous studies had estimated kidney damage was experienced by more than a fifth of all hospitalized with the illness and more than half of those hospitalized from the virus in the ICU. Earlier research had also learned that a third of all patients with COVID-19-related kidney damage had not recovered after three weeks following discharge.

The latest study, which was conducted by nephrologists from Yale, adds another log to the bonfire of the notion that catching COVID-19 is either deadly or not. For some, COVID-19 can leave you with a third outcome: long-term, sometimes debilitating illness.

In the case of COVID-19-triggered kidney disease, that can mean a chronic condition requiring dialysis and potential organ transplant, although its remains too early to know if a rise in organ failure will become a future legacy of the pandemic.

The Yale study looked at outcomes for more than 1,600 patients with acute kidney injury following hospitalization for any reason between March and September of 2020, comparing those with COVID-19 to those without. People with the virus are discharged when their breathing improves, but that itself is not an indicator of kidney function.

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The authors discovered that patients with COVID-19 had a decline upon discharge of about 15%, and unrelated to preexisting health problems.

Black and Hispanic patients with COVID-19 were hit especially hard. They had nearly three times the kidney disease associated with hospitalization for COVID-19 than for other reasons.

Given the unknown final course of this decline, the authors counseled post-hospitalized COVID-19 patients to monitor a proxy for kidney health known as the GFR slope, a metric tested by checking creatinine levels in the blood and urinalysis showing elevated protein and blood.

On the whole, kidney disease is silent and can't be cured, experts say, meaning those who have it require careful management to slow progression.

"People with kidney disease are pretty asymptomatic," says Mayo Clinic kidney specialist Dr. Andrew Bentall. "They can be down to 15-20% function and they don't really feel any symptoms."

"Kidney disease is one of the diseases that people don't know anything about until it's severe, sometimes so much that they would then need dialysis or transplantation at the most severe point."

Dr. Andrew Bentall is a nephrologist at the Mayo Clinic. Submitted photo
Dr. Andrew Bentall is a nephrologist at the Mayo Clinic. Submitted photo

COVID-19 damages kidneys through multiple pathways.

All serious illnesses can tax the vital organs through dehydration and other penalties of sickness. Viruses such as strep throat and hepatitis can and do damage kidneys. On top of this risk, the SARS-CoV-2 virus itself attaches to ACE2 receptors that control blood pressure and line the organ.

"People get low oxygen levels," adds Bentall. "Twenty percent of the blood from the heart goes to the kidney. You can imagine if there's less oxygen in the blood leaving the heart, less is going to get sent to the kidney, and the kidneys are really sensitive to oxygen levels."

Additionally, an overactive immune system in response to the virus causes inflammatory damage.

"There seems to be this combination with COVID-19 that it's very immunogenic," Bentall says. "It creates a cytokine release, this inflammation that's probably creating damage to the kidney vessels and that starts a proliferation of other things going wrong."

Also, the virus can causes clots which clog the vascular system within the organ.

For those without COVID-19 hospitalization, doctors sometimes recommend checking for kidney function via annual checkups, although the physicals themselves are increasingly considered outdated according evidence-based treatment guidelines.

Given its connection to high blood pressure, diabetes and other metabolic conditions assessed during routine health visits, kidney disease often can be identified in the course of standard care. Providers in 2020 have become concerned however that the pandemic has cut in on routine health visits.

Either way, it's become increasingly clear that COVID-19 is to be avoided, whether or not you are at risk of serious illness.

"I've met colleagues and patients who have had COVID-19 and developed post-COVID fatigue," Bentall says. "People are left with shortness of breath. There's lung scarring from COVID. They've survived, they haven't died, but they're struggling to function as they did before."

"Kidney damage (following COVID-19) is likely to be longer-term," he cautions. "Kidneys don't regenerate very well. They don't regenerate at all."