A new study has found that most routine laboratory tests are not reliable for diagnosing Long COVID, also known as Post-Acute Sequelae of SARS-CoV-2 infection (PASC).
The study, published in Annals of Internal Medicine, found no reliable biomarker among 25 routine clinical laboratory values for prior infection, PASC or specific types of PASC clusters. This suggests none of these routine tests can serve as a clinically useful biomarker of PASC.
The study's first author, Kristine Erlandson, MD, a professor in the Division of Infectious Diseases at the University of Colorado Anschutz Medical Campus, commented: "Our study shows patients can have severe Long COVID with normal laboratory results. This suggests doctors should not focus on the results of blood panels to diagnose Long COVID but should focus more on symptoms and ways to help patients get relief by treating their symptoms."
According to Agency for Healthcare Research and Quality’s Medical Expenditure Panel Survey, 7% of all adults in the US, nearly 18 million people, currently have Long COVID
“Our challenge is to discover biomarkers that can help us quickly and accurately diagnose long COVID to ensure people struggling with this disease receive the most appropriate care as soon as possible,” said David Goff MD PhD, director for the Division of Cardiovascular Sciences at the NIH’s National Heart, Lung, and Blood Institute. “Long COVID symptoms can prevent someone from returning to work or school, and may even make everyday tasks a burden, so the ability for rapid diagnosis is key.”
To investigate clinical laboratory markers of SARS-CoV-2 and PASC, the researchers examined data from nearly 10,000 adults with and without SARS-CoV-2 infection. The researchers recruited from over 80 enrolling sites across 33 US states plus Washington, DC and Puerto Rico, making it one of the largest and most diverse studies of its kind.
The study compared results in several ways: between participants with and without prior SARS-CoV-2 infection at six months after infection, between participants with and without PASC and between participants with each of four most common PASC symptom phenotypes and those unlikely to have PASC.
They found participants with prior SARS-CoV-2 infection showed modest increases in HbA1c (a marker of long-term blood sugar levels) and urinary albumin-to-creatinine ratio (uACR), along with small decreases in platelet counts.
The researchers suggest this data shows the complexity of PASC as a condition that may involve multiple physiological pathways beyond simple laboratory markers, such as those for inflammation, anaemia or other markers.
“Long COVID has been very elusive; numerous possible symptoms, no definite cause and no clear treatment. We hear from patients that their concerns are dismissed by providers because their test results are normal. In this study, even the exhaustive list of routine blood tests could not help in making a PASC diagnosis. This is an important observation in PASC research as prior smaller studies showed inconsistent abnormalities in some blood tests. Until a reliable biomarker is found, the best diagnostic modality for PASC remains the old-fashioned history taking and clinical assessment,” commented Grace McComsey, MD, senior author of the paper, Professor and Vice Dean of Clinical and Translational Research at Case Western Reserve University.
- Erlandson KM, Geng LN, Selvaggi CA, et al. Differentiation of Prior SARS-CoV-2 Infection and Postacute Sequelae by Standard Clinical Laboratory Measurements in the RECOVER Cohort. Ann Intern Med. Published online August 13, 2024. doi:10.7326/M24-0737