Since 2021, the US National Institutes of Health (NIH) has enrolled 90 000 people across more than 200 clinical sites as part of its RECOVER initiative to understand, identify, and treat post-COVID-19 condition, also known as long COVID. One goal of these studies has been to discover biomarkers that can help diagnose long COVID because symptoms are so wide-ranging. Recently, though, a study in the Annals of Internal Medicine found that routine laboratory tests are unlikely to help achieve that goal.

More than 10 000 adults across 83 clinical sites took part in the study, including people who hadn't had COVID-19, those who had been infected, and about 1800 who currently had long COVID. At enrollment, the researchers carried out 25 common laboratory tests -- such as complete blood cell counts, metabolic panels, hemoglobin A and high-sensitivity C-reactive protein values, and urinalysis -- for all participants, who also underwent a physical examination. All were followed up over a 2-year period.

The researchers found no meaningful differences in the laboratory results for people across the 3 groups. The study's results suggest that clinicians are left to continue to order tests to "rule out alternative explanations rather than diagnose long COVID," the authors of an accompanying editorial wrote.