August 13, 2025
Engin Akyurt/Pixabay
More than 200 symptoms, such as brain fog and fatigue, are associated with long COVID. But a lack of a universal definition of the condition is hindering treatment, a new study says.
A vast discrepancy in how researchers define long COVID is hindering understanding and treatment of the disease, a new study suggests.
“Without a clinically usable and standardized research definition of Long COVID, it’s like every study is using a different measuring stick,” Dr. Joann Elmore, a professor at UCLA's David Geffen School of Medicine and the study's lead author, said in a release. “Without a shared definition, we risk mislabeling patients and misguiding care. This is more than an academic debate — it affects real people.”
Long COVID, sometimes called long-haul COVID, generally refers to adverse health effects that last three months or longer after infection with COVID-19. But scientists and medical experts have not come up with a universal definition for the condition. Studies have associated it with more than 200 different symptoms including extreme fatigue, issues with taste and smell, digestive problems, mood disorders and heart disease, according to the Mayo Clinic.
The number of people identified as having long COVID varied widely – between 15% and 42% in the same group – depending on what definition of the condition was used, according to the new study published Tuesday in JAMA Open Network.
The five different definitions lacked "sensitivity," meaning the way they identified long COVID did not align well with how patients reported their own symptoms. Some people are likely being misdiagnosed and others not identified as having the condition because of scientists have not reached consensus on an interpretation of long COVID, the study said.
“In the absence of an objective measure, like a blood test, or a uniform standard for measuring Long COVID, researchers and clinicians will need to decide which definition is best suited for their scientific question and be more transparent about the potential limitations of using a more vs less restrictive definition,” Lauren Wisk, an assistant UCLA medical professor who also led the new study, said in the release.
The study used data collected from 4,700 COVID patients involved in ongoing research and employed five different published definitions of long COVID from the United States, United Kingdom, Sweden, Netherlands and Puerto Rico.
The definitions differed in how long the studies defined long COVID as lasting, ranging from four weeks to six months, and each encompassed anywhere from nine and 44 symptoms.
