Long COVID with Symptoms Persisting for More than Six Months in Unvaccinated Patients: Investigation of Biochemical Changes Associated with Chronic Manifestations

Long COVID is a complex condition characterized by persistent symptoms following SARS-CoV-2 infection. Understanding its biochemical mechanisms is essential for effective management and treatment strategies. Objective: This study investigated biochemical alterations associated with long COVID in unvaccinated individuals presenting symptoms persisting for more than six months, highlighting the prolonged nature of the condition and its systemic and neurological manifestations. A cross-sectional study was conducted with 60 unvaccinated patients at least six months post-COVID-19 infection. Serum biomarkers, including C-reactive protein (CRP), interleukin-6 (IL-6), N-terminal pro-brain natriuretic peptide (NT-proBNP), and irisin, were analyzed. Correlations between these biomarkers and persistent symptoms were assessed using statistical regression models. Elevated CRP levels were significantly associated with persistent respiratory and musculoskeletal symptoms, suggesting ongoing inflammation. Increased IL-6 levels correlated with fatigue and musculoskeletal complaints. NT-proBNP elevations were linked to cardiovascular manifestations, including dyspnea and chest pain. A positive correlation between irisin and persistent sensory impairments, such as anosmia and dysgeusia, indicates potential neuroinflammatory mechanisms. This study highlights that persistent inflammation plays a critical role in long-term (>6 months) post-COVID manifestations. Monitoring biomarkers such as CRP, IL-6, NT-proBNP, and irisin may enhance understanding and management of prolonged post-COVID conditions.