A new study has found millions of COVID patients may have undiagnosed acute kidney injury (AKI).

Acute kidney injury is a condition where the kidneys suddenly fail to filter waste from the blood, which can lead to serious illness or even death. Existing data indicates approximately 20% of patients admitted to hospital with COVID develop AKI, rising to roughly 40% for those in intensive care, according to the study from the University of Queensland.

But UQ PhD candidate and kidney specialist Marina Wainstein says the true numbers could be double those figures.

“Doctors look at the amount of urine a patient passes and the level of a compound called creatinine in the blood, which rises when the kidneys aren’t working well,” she says. “However, if that creatinine rise occurs before a patient presents to hospital, we can miss the AKI diagnosis and fail to manage the patient appropriately in those early, critical days of hospitalization.”

Wainstein says when researchers also measured the fall in creatinine levels, which often follows the initial rise, the rate of AKI diagnosis in COVID patients doubled.

“That was a pretty shocking finding,” she says.

Wainstein says “missing” AKI in COVID patients is dangerous.

“Even though the AKI is already starting to improve in hospital, our research shows that these patients have worse in-hospital outcomes and are more likely to die compared to patients with no AKI,” she says.

Wainstein says treatment for AKI can be as simple as checking a patient’s hydration level and stopping medications that can be toxic to the kidneys.

Study supervisor Sally Shrapnel, PhD, from UQ’s School of Mathematics and Physics, says collecting and analyzing data for the project during the pandemic proved challenging.

“Typically data scientists work with complete, well curated registry data, but in this project it was collected by hospital staff working under extremely onerous conditions in a variety of different resource settings,” she says. “Curating and cleaning the data turned out to be a significant part of the project.”

Shrapnel said the researchers were able to include data from resource-poor countries, where community-acquired AKI is also more common.

“These people have limited access to healthcare and are more likely to present late in the disease process,” Shrapnel says.

Shrapnel says a more comprehensive definition of AKI—one which can detect cases that develop in the community—needs to be implemented as soon as possible.

“Now we have the data showing a large gap in AKI diagnosis exists, it’s time to test this definition in a clinical trial so we can identify all AKI patients early and hopefully prevent these awful outcomes,” Shrapnel says.

The research is published in PLOS Medicine.