Routine lab tests fail to detect long COVID in 10,000-person study

Dive Brief:

A study of more than 10,000 people found no evidence that any of 25 routine laboratory tests can detect long COVID.
The study, published Tuesday in the Annals of Internal Medicine, aimed to show whether COVID-19 causes persistent changes in biomarkers and, if so, whether tests can augment symptom-based definitions of long COVID.
While the researchers saw small differences in lab results between patient cohorts, the variation could be due to chance and the findings were largely not clinically meaningful. The outcome led the authors to conclude routine laboratory tests are not useful biomarkers for long COVID.

Dive Insight:

The study analyzed samples from 10,094 people enrolled in the National Institutes of Health’s Recover Initiative. The samples came from people with and without prior infection. Within the group of people with prior infections, researchers previously identified symptom-based long COVID subtypes. The samples allowed the latest study to compare lab results between patients with different histories.

On average, people who had been infected scored differently on some tests, such as platelet count, than their counterparts who never had COVID-19. However, the researchers found no clinically meaningful differences between people with high and low scores on a long COVID severity scale.

Exploratory models identified some biomarkers associated with subtypes of long COVID. High-sensitivity C-reactive protein was elevated in people with smell or taste impairments and in another subtype with symptoms such as brain fog. However, the authors questioned whether the results were due to chance and said they were “largely not clinically meaningful.”

The researchers concluded even patients with highly symptomatic long COVID may have “no clinically observable objective findings on routine laboratory testing.” Routine tests still have a role in ruling out other treatable causes of symptoms but, based on the study, have little use as biomarkers of long COVID.

Studies will likely need to go beyond routine lab tests to understand the biological basis of the condition, the authors said, for example by using transcriptomics, proteomics and metabolomics to identify novel biomarkers.