Routine lab tests ineffective in diagnosing Long COVID

Long COVID difficult to detect: ©Parradee - stock.adobe.com

A study published in the Annals of Internal Medicine has found that routine laboratory tests commonly used in clinical practice are not reliable for diagnosing Long COVID, also known as Post-Acute Sequelae of SARS-CoV-2 infection (PASC). The study, which is one of the most extensive and diverse of its kind, revealed a lack of reliable biomarkers among 25 routine clinical lab values for detecting prior SARS-CoV-2 infection or diagnosing various forms of PASC.

The research, conducted by a team from the University of Colorado Anschutz Medical Campus, analyzed data from nearly 10,000 adults across 33 U.S. states, Washington, DC, and Puerto Rico. The study compared participants with and without prior SARS-CoV-2 infection six months post-infection, as well as those with and without PASC. Despite modest differences in certain lab values, such as HbA1c and urinary albumin-to-creatinine ratio, the study concluded that these variations were too small to serve as diagnostic tools for Long COVID.

"Our study shows patients can have severe Long COVID with normal lab results," said Kristine Erlandson, M.D., the study's first author and a professor at CU Anschutz. "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."

Long COVID continues to be a significant health concern, affecting approximately 7% of adults in the U.S., or nearly 18 million people, according to the Agency for Healthcare Research and Quality. The inability to diagnose PASC through routine lab tests presents a challenge for health care providers.

"Our challenge is to discover biomarkers that can help us quickly and accurately diagnose Long COVID," said David Goff, M.D., 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."

The study, funded by the National Institutes of Health’s RECOVER Initiative, underscores the complexity of Long COVID as a condition that may involve multiple physiological pathways beyond simple lab markers. The research team emphasized the importance of clinical assessment and patient history in diagnosing the condition.

“Long COVID has been very elusive; numerous possible symptoms, no definite cause, and no clear treatment,” said Grace McComsey, M.D., senior author of the paper and vice dean of clinical and translational research at Case Western Reserve University. “In this study, even the exhaustive list of routine blood tests could not help in making a PASC diagnosis. Until a reliable biomarker is found, the best diagnostic modality for PASC remains the old-fashioned history taking and clinical assessment.”

While the study highlights the limitations of routine lab tests, the researchers said that these tests are still essential for ruling out other conditions during the diagnostic process for PASC. As the search for reliable biomarkers continues, health care providers are encouraged by the researchers to focus on symptom management and patient-centered care in the treatment of Long COVID.