COVID source shout-out: Moving closer to Long COVID biomarkers

Scientists are moving closer to biomarkers, or clear biological indicators, of Long COVID. A new study—posted this week in Nature ahead of full publication—identifies clear differences between blood samples of people who have the condition and those who don’t.

The study was a collaborative effort between researchers at Mount Sinai (David Putrino and his team) and Yale University (Akiko Iwasaki and her team). Both of these research groups have been leaders in studying Long COVID: Mount Sinai was one of the first health institutions to start caring for people with Long COVID back in spring 2020, while the Yale group has analyzed patients’ immune systems in ways that go far beyond typical medical testing.

The differences identified by this study fall into “three big areas,” Putrino wrote in a Twitter thread describing the findings. These are hormonal differences (particularly low cortisol levels in the Long COVID group during morning hours), immune differences (particularly differences in T cell and B cells for people with Long COVID), and evidence of a coronavirus infection re-activating other viruses that might have already been present in people with Long COVID.

While other research has pointed at these Long COVID markers before, the new study goes further in connecting a Long COVID diagnosis to specific medical tests. If backed up by further research, those tests could be used as biomarkers, informing clinical trials of Long COVID treatments. Notably, as Iwasaki pointed out in a statement, the tests done in this study would not be included in a patient’s “routine lab work,” signifying the higher level of inquiry needed to understand this condition.

Long COVID is incredibly complex and may have different causes from one person to another. So, any biomarkers (from this study or another one) likely would not be universal points of success for all patients. This study also isn’t “proof that Long COVID is real,” as you might have seen some headlines suggest; we’ve had plenty of proof for years now, from prior research and patient experiences. Still, the study is a major step forward in identifying key tests that may be used for diagnosis and treatment.