A new study from the National Institutes of Health (NIH) highlights the difficulty of finding a lab test for long Covid — a new condition that includes dozens of symptoms and is currently considered a “diagnosis of exclusion.”
The most common symptoms of Long Covid are brain fog, fatigue and palpitations, which can change over time and can be disabling if severe. About one in 20 adults reported persistent symptoms of Covid, so far June 2024.
The study followed patients for four years and included a battery of standard lab tests, but found “remarkably few” differences between people who had long-term Covid and those who did not.
“Covid is just the latest example of an infectious disease that can cause post-infectious fatigue syndrome,” Dr. Paul G Auwaerter, professor of medicine and director of the division of infectious diseases at the Johns Hopkins University School of Medicine and a researcher of Lyme disease.
This study addressed one of the major mysteries of long Covid: finding a “biomarker” that could help doctors develop a diagnostic test, rather than ruling out other possible diseases, as they do now.
“Our challenge is to discover biomarkers that can help us diagnose long COVID quickly and accurately so that people struggling with this disease can get the most appropriate care as quickly as possible,” said Dr. David Goff, director of the division of cardiovascular sciences at the NIH’s National Heart, Lung and Blood Institute.
“Long-term Covid symptoms can prevent someone from going to work or school, and can even make daily tasks a burden, so it’s important to get a diagnosis early.”
The research, published in the Annals of Internal Medicinestudied more than 10,000 adults at 83 clinical sites in the US between 2021 and 2023. About 1,800 participants met the researchers’ definition of long-term Covid.
Participants were given a panel of 25 standard blood and urine tests in the study, starting six months after infection or when they enrolled. They were followed for four years. As in 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 Covid and those who did not meet the criteria. Researchers found a modest association with HbA1c, a measure of average blood sugar levels over two to three months, but the association disappeared when they controlled for pre-existing diabetes.
They also considered a test that showed kidney function was slightly lower in some participants, but this metric occurred in only a minority of patients and may be a result of an initial Covid-19 infection.
Part of the challenge of finding or developing a long Covid lab test, Auwaerter said, was that scientists still don’t understand the mechanisms underlying chronic fatigue syndromes in general. Particularly those, like Covid, that “preferentially affect (middle-aged women).” That makes finding a diagnostic test “even more of a challenge.” Auwaerter called the task “Herculean” in a editorial that accompany the new study.
One key difference in the research space is funding. The series of Recover studies now underway, including ambitious, large-scale efforts to study electronic medical records, autopsies, and large observational studies, are all being paid for with a $1.1 billion budget from Congress. More funding will likely be needed if society is to make further progress.
“The hunt will continue,” Auwaerter said, and there will likely be a move to tests that are currently used only for research, to see if they can “shed light or provide clinicians with a diagnosis.”