Long COVID is a lingering condition that affects 5-20% of people who have had COVID. There have been over 200 documented symptoms of Long COVID, including fatigue, brain fog, and joint pain. A recent study found that people with Long COVID have immune response markers in their blood that should have gone away after infection. This is an exciting discovery, but many more large-scale studies are needed to find out if a blood test can accurately detect Long COVID.

Long COVID is a real illness and a term used to describe a wide range of health problems and symptoms that persist after a COVID infection. It is more likely to occur in people who have had a severe COVID infection and in non-vaccinated individuals, but anyone who gets a COVID infection is at risk for developing Long COVID.

Scientists do not know what causes Long COVID, and there has been a lot of research examining the blood makeup of people who have the illness to search for a “biomarker” or something in the blood that most of these patients have in common, and is not present in people without Long COVID.

A study published in January 2024 analyzed over 7,000 protein components in the blood of 40 people who developed Long COVID for up to 1 year after initial COVID infection. The study found that compared to people who fully recovered from a COVID infection, the Long COVID patients had what is called a “dysregulation complement”.

A “complement” is a collection of immune proteins that get chopped up during an infection and send a signal to the body to fight off a disease. In the short-term, this fights off an illness and the chopped-up proteins should disappear. The presence of these proteins long-term can cause damage to the cells.

Finding these chopped-up proteins in the blood of patients with Long COVID suggests this could be a possible biomarker, but more large-scale studies are needed.

Scientists are still learning what causes Long COVID, and it is likely a combination of factors and not one specific thing. Some hypotheses include tissue damage, viral reservoirs, autoimmunity, and persistent inflammation.

Healthcare professionals are still learning how to diagnose Long COVID in patients who present with symptoms similar to many other health disorders.

Researchers hope that by finding biomarkers of Long COVID, a blood test could be used for diagnosis and scientists could be one step closer to developing potential treatment options. These possibilities are still a long way off, but the findings of this study are one step in that direction.