Long Covid continues to elude a clear diagnostic test, researchers reported in a study published Monday in the Annals of Internal Medicine.
The findings are part of the National Institute of Health’s RECOVER initiative, a more than $1 billion effort launched in 2021 to investigate the causes and treatments for the estimated 17 million Americans with long Covid.
Monday’s study used data from more than 10,000 patients at 83 clinical sites across the country. The researchers looked at a range of patients’ lab results, including routine blood counts, kidney and liver test results, and markers of inflammation in the body. They found no difference between people with long Covid and those without it.
Dr. Kristine Erlandson, lead author of the study and an infectious disease physician at the University of Colorado Anschutz Medical Campus, said she was disappointed they couldn’t find a test that could tell doctors about long Covid.
“I think that’s consistent with what we’ve learned more recently,” Erlandson said. “This is really a symptom-driven disease and there’s no specific lab value that points us toward that definition or toward diagnosing someone with long Covid.”
In an accompanying editorial, physicians at Johns Hopkins University School of Medicine wrote: “Clinicians should continue to do what we have done in the past: order tests to rule out other explanations rather than to diagnose long COVID.”
Patients in the study were classified as having long Covid based on a 12-symptom scoring system, including brain fog, dizziness, and palpitations, among others. Different symptoms were assigned different scores, and a diagnosis of long Covid was made if the score reached a level of 12.
There was no time limit for the onset of symptoms and a positive Covid test was not required for diagnosis.
Dr. Marc Sala, a pulmonologist and co-director of Northwestern Medicine’s Comprehensive Covid Center, said the study was well-conducted but noted the results could be frustrating for the millions of people still suffering from the disease.
“I think one of the criticisms that can be leveled at the study is that a lot of these tests that they sent out are the same tests that you get from your primary care physician,” Sala said. “A lot of these tests were not exactly tailored to looking for a new cause of long Covid.”
Sala said that while routine blood tests are often normal in his patients with long Covid, more specialized tests — such as blood tests while a patient is exercising or a CT scan after Covid pneumonia — are showing up abnormal. He added that patients, especially those who are otherwise healthy and who come in with extraordinary shortness of breath and fatigue, would need far more testing than was done in the paper.
Erlandson, the study’s author, said this research is a first step and that more specialized testing is being done as part of additional research for the RECOVER Initiative.
Dr. Nisha Viswanathan, director of the Long Covid Clinic at UCLA Health, was not surprised by the results, given her experience working with long Covid patients for three years.
“One of the most striking things about long Covid is the fact that at least our standard medical tests have come back negative, while our patients are struggling with persistent symptoms,” Viswanathan said.
She said she hopes there will one day be a biomarker for long Covid, citing as a potential clue a recent preprint, or non-peer-reviewed study, from Yale School of Medicine showing high levels of autoantibodies, or antibodies that attack the body instead of intruders.
