Known as the red cell distribution width (RDW) test, it measures the range in the volume and size of red blood cells.
The RDW test is usually used to help diagnose various medical conditions such as anaemia, heart disease, blood disorder and diabetes.
But researchers at Massachusetts General Hospital in Boston, US, said they were “surprised” to find that RDW was “highly correlated with patient mortality” in Covid-19 cases.
Such discoveries could point to new treatment strategies or identify better markers of disease severity
Dr Jonathan Carlson, of Massachusetts General Hospital, who is one of the authors on the study published in the journal Jama Network Open, said: “The correlation persisted when controlling for other identified risk factors like patient age, some other lab tests, and some pre-existing illnesses.”
The researchers analysed medical data of 1,641 adults who were diagnosed with Covid-19 infection and admitted to a hospital in the Boston area between March 4 and April 28 2020.
The team then used different blood tests to look for “complicated changes” in circulating blood cells.
Senior author Dr John M Higgins, an investigator in the department of pathology at Massachusetts General Hospital, said: “We wanted to help find ways to identify high-risk Covid patients as early and as easily as possible – who is likely to become severely ill and may benefit from aggressive interventions, and which hospitalised patients are likely to get worse most quickly.”
The researchers found that those with RDW values above the normal range were nearly three times as likely to die after being infected with coronavirus, compared with Covid-19 hospital patients with normal RDW values.
A subsequent increase in RDW after hospital admission was associated with an even higher risk of dying, the researchers said.
They add that regularly monitoring RDW of Covid-19 patients could help determine whether they are responding to treatment or getting worse.
As part of the next steps, the team is now looking to understand the biological mechanisms that cause RDW elevations in severe Covid-19 cases.
Dr Aaron Aguirre, a cardiologist and critical care physician at Massachusetts General Hospital, said: “Such discoveries could point to new treatment strategies or identify better markers of disease severity.”
