Searching for biomarkers of long COVID: findings from a nationwide population-based study

Long COVID, characterized by persistent symptoms following SARS-CoV-2 infection, affects an estimated 400 million people worldwide. The absence of reliable biomarkers has hindered progress toward targeted therapies. We investigated potential biomarkers of long COVID in a nationwide study of people in the Faroe Islands ( n = 218, aged ≥ 15 years) who were infected with SARS-CoV-2 during the spring (wave 1, n = 101) and autumn (wave 2, n = 117) of 2020. Although we investigated a multitude of possible clinical, neurological, and paraclinical biomarkers, no convincing biomarker was found. We found that lower INR was associated with long COVID (adjusted odds ratio 0.66, 95% confidence interval 0.46–0.95, p = 0.03), but despite the statistically significant association, no clinical significance was observed because all INR values were within the normal range.