Association between chemosensory dysfunctions and inflammatory biomarkers in patients with SARS-CoV-2 infection: a systematic review and meta-analysis

BACKGROUND: There is evidence that chemosensory dysfunctions, including smell and taste disorders, are common findings in patients with SARS-CoV-2 infection. However, the underlying biological mechanisms and the role of inflammatory markers are still poorly understood. AIM: To investigate the inflammatory biomarkers levels in patients with COVID-19 presenting chemosensory dysfunctions. METHODS: This review was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guideline. A systematic literature search was performed from January 1, 2020, to May 12, 2022. Observational studies that provided data on hematological, biochemical, infection-related indices and cellular immunity, and coagulation function in patients with COVID-19 experiencing smell and/or taste disorders were considered eligible. Effect sizes were reported as standardized mean difference (SMD) with 95% confidence intervals (CI). A negative effect size indicated that the inflammatory biomarker levels were lower among patients with chemosensory dysfunctions. RESULTS: Eleven studies were included. Patients with chemosensory disturbances had lower levels of leukocytes (SMD − 0.18, 95% CI − 0.35 to − 0.01, p = 0.04), lactate dehydrogenase (SMD − 0.45, 95% CI − 0.82 to − 0.09, p = 0.01), IL-6 (SMD − 0.25, 95% CI − 0.44 to − 0.06, p < 0.01), and C-reactive protein (SMD − 0.33, 95% CI − 0.58 to − 0.08, p < 0.01) than patients without chemosensory disturbances. CONCLUSION: Patients with SARS-CoV-2 infection who have olfactory and gustatory disorders have a lower inflammatory response than patients who do not have chemosensory alterations. The presence of these symptoms may indicate a more favorable clinical course for COVID-19. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s10787-022-01066-z.