Biomarker Blood Test Could Predict Development of Long COVID

Long COVID continues to challenge scientists and clinicians with its complex and poorly understood symptoms that can persist long after an acute SARS-CoV-2 infection. While most immune responses normalize within weeks after recovery, some patients continue to experience fatigue, inflammation, and organ dysfunction months later. The biological mechanisms underlying these long-term effects remain unclear. Now, a new study has identified a blood-based immune biomarker that may predict prolonged tissue damage and persistent inflammation in such patients.

Researchers at the Medical University of Vienna (MedUni Vienna, Vienna, Austria) conducted a study to investigate components of the innate immune system known as acute phase proteins, which rapidly rise during infection. The team analyzed blood samples from 141 COVID-19 convalescent patients at 10 weeks and 10 months after infection and compared them with samples from 98 uninfected controls. The aim was to determine whether any of these immune proteins remained elevated beyond the recovery period, indicating ongoing immune activation or tissue repair.

Image: The potential biomarker could identify existing tissue damage, long-term immune activation and complications following COVID-19 (Photo courtesy of 123RF)

The study, published in Frontiers in Immunology, revealed that levels of the protein pentraxin 3 (PTX-3) remained significantly higher in individuals who had experienced severe COVID-19, even months after recovery. Elevated PTX-3 levels were observed at both 10 weeks and 10 months post-infection, unlike other acute-phase proteins that typically return to normal within days. This persistence suggests that PTX-3 could serve as a biomarker for chronic inflammation or residual tissue injury associated with long COVID.

The findings support previous evidence linking PTX-3 to severe acute COVID-19 but extend its relevance to long-term recovery. Persistent high levels of PTX-3 may signal the presence of ongoing repair processes or residual viral remnants in the body. These insights add to growing evidence that sustained immune activation contributes to the symptoms of long COVID and conditions such as myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS).

Researchers believe that identifying PTX-3 as a potential biomarker could enable earlier diagnosis and monitoring of post-COVID complications. The study also emphasizes the need for follow-up care in patients recovering from severe infections and underscores the importance of understanding immune system regulation in long-term COVID recovery. Future research will aim to confirm these findings in larger, prospective studies and further clarify the biological pathways involved.

“We assume that the higher PTX-3 levels either indicate ongoing tissue repair mechanisms or could hint at the presence of persistent SARS-CoV-2 remnants in the body. PTX-3 could thus serve as a biomarker for long-lasting tissue damage and long-term immune activation resulting in possible complications after COVID-19,” said Professor Winfried Pickl, who led the research group.

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