A new study by the National Institute of Health (NIH) highlights the difficulty of finding a laboratory test for prolonged Covid – a new condition that includes dozens of symptoms and is currently considered a “diagnosis of exclusion”.
Lung Covid’s most common symptoms include brain fog, fatigue and palpitations, which can change over time and can be disabling when severe. About one in 20 adults reported persistent symptoms of Covid June 2024.
The study followed patients for four years and included a series of standard laboratory tests, but found that there were “significantly few” differences between people who had had Covid for a long time and those who had not.
“Covid is just the latest example of an infectious disease that can cause post-infectious fatigue syndrome,” Dr. Paul G Auwaerter, a professor of medicine and director of the division of infectious diseases at Johns Hopkins University School of Medicine and a Lyme disease researcher.
This study focused on one of the long-standing Covid’s key mysteries – finding a “biomarker” that could help doctors develop a diagnostic test, rather than ruling out other possible diseases as is the case today.
“Our challenge is to discover biomarkers that can help us diagnose long-term Covid quickly and accurately to ensure that people struggling with this disease receive the most appropriate care as soon as possible,” says Dr David Goff, director for the division of cardiovascular sciences at the NIHs. National Heart, Lung, and Blood Institute.
“Prolonged Covid symptoms can prevent someone from returning to work or school, and can even make everyday tasks a burden, so the ability for rapid diagnosis is key.”
The research, published in the Annals of Internal Medicinelooked at more than 10,000 adults across 83 clinical sites in the US between 2021 and 2023. About 1,800 participants met the researchers’ definition for prolonged Covid.
Participants received a panel of 25 standard blood and urine tests in the study either starting six months after infection or when they enrolled. They were followed for four years. Like other long Covid studies, the majority of participants were middle-aged women. The group was considered racially diverse.
Scientists found few differences between people diagnosed with long-term Covid and those who did not meet the criteria. Researchers found a modest association with HbA1c, a measure of average blood sugar over two to three months, but the association disappeared when they controlled for pre-existing diabetes.
Similarly, they considered a test that showed a slightly lower kidney function for some participants, but the measure appeared in only a minority of patients and could be the result of the initial Covid-19 infection.
Part of the challenge in finding or developing a lengthy Covid lab test, Auwaerter said, was that scientists still don’t understand the mechanisms underlying chronic fatigue syndrome in general. Especially those, like Covid, who “prefer [affect] women in middle age”. This makes finding a diagnostic test “even more of a challenge”. Auwaerter called the task “herculean” in a editorship which accompanies the new study.
One key difference in the research space is funding. The series of Recover studies now underway, including ambitious and large-scale efforts to study electronic health records, autopsies and large observational studies, are all being paid for with a $1.1bn budget from Congress. More funding is likely to be needed if society is to progress further.
“The hunt will continue,” Auwaerter said, likely moving toward tests that are currently only used for research to see if they “can shed light or provide clinicians with a diagnosis.”
