Circulating calprotectin as a potential biomarker of persistent olfactory dysfunctions in Post-COVID-19 patients

Background: This longitudinal prospective study aims to investigate the potential of circulating calprotectin (cCLP) as a biomarker in persistent olfactory dysfunctions following COVID-19 infection. Methods: Thirty-six patients with persistent hyposmia or anosmia post COVID-19 were enrolled (HT0) and reevaluated after three months of olfactory training (HT1). Two control groups included 18 subjects without olfactory defects post COVID-19 (CG1) and 18 healthy individuals (CG2). Nasal brushing of the olfactory cleft and blood collection were performed to assess circulating calprotectin levels. Results: Higher calprotectin levels were observed in serum and nasal supernatant of hyposmic patients (HT0) compared to control groups (CG1 and CG2). Post-olfactory training (HT1), olfactory function improved significantly, paralleled by decreased calprotectin levels in serum and nasal samples. Circulating calprotectin holds potential as a biomarker in persistent olfactory dysfunctions after COVID-19. The decrease in calprotectin levels post-olfactory training implies a role in monitoring and evaluating treatment responses. Discussion and Conclusions: These findings contribute to the growing literature on potential biomarkers in postCOVID-19 olfactory dysfunctions and underscore the importance of investigating novel biomarkers for personalized patient management. Nevertheless, further studies are needed to validate the application of calprotectin assay in nasal diseases and its correlation with nasal cytology.