The confounding mystery behind what causes Long COVID as well as developing definitive tests to identify and diagnose the condition has been an ongoing frustration for public health officials, clinicians, and patients.
New research, however, looks to shed some light into characteristics of Long COVID. Specifically, blood serum proteins might offer a key to diagnosing Long COVID. A study published in Science showed that patients experiencing Long COVID, “exhibited changes to blood serum proteins indicating activation of the immune system’s complement cascade, altered coagulation, and tissue injury.”
Study Parameters and Findings
This was a multicenter study, which consisted of 39 healthy control patients and 113 COVID-19 patients who were followed-up to 1 year after initial confirmation of infection through PCR test. After confirmation of acute infection, patients were seen for follow-up appointments at 6 months and 12 months to identify biomarkers associated with Long COVID. At the 6-month follow-up, 40 patients had Long COVID symptoms.
The investigators noted that this group that had Long Covid at 6 months showed a higher prevalence of severe acute COVID-19 compared with the 73 other COVID-19 patients.
Blood serum was collected from both the healthy control cohort and the COVID-19 patient cohort during the acute COVID-19 stage and at 6-month follow-up.
From that, investigators detected differences in serum protein levels from those with severe COVID-19 and those with a milder form. And differences in those with Long COVID and those who did not have it at both the time of acute infection and at the 6 month follow-up.
The investigators noted that in patients who experience severe COVID-19 there can be associations such as autoantibody formation and persistent inflammation after recovery of the acute infection and can confound Long-COVID-associated changes. As such, they searched for differences in the serum.
They found distinctions in the complement system, which is made up of plasma proteins.