Objective: The aim of this study was to evaluate the clinical relevance of absolute eosinophil blood count and eosinophil count by nasal cytology in the context of real-life clinical practice and to determine if they correlate with the severity of symptoms in patients with chronic rhinosinusitis with nasal polyps (CRSwNP).

Methods: We enrolled 425 patients with CRSwNP followed between January 2015 and April 2023 at the A. Gemelli Hospital Foundation-IRCCS, Rome, Italy. We gathered data on blood and local eosinophil count and correlated the results with clinical features. All patients underwent endoscopy, Visual Analogical Scale (VAS) for main symptoms, and SinoNasal Outcome Test 22 (SNOT-22).

Results: We observed significantly higher mean levels of eosinophils in serum and at nasal cytology in patients with CRSwNP and comorbidities (asthma, non-steroidal anti-inflammatory drugs - exacerbated respiratory disease and allergy) compared to those without. Blood eosinophilia was not associated with severity of symptoms, whereas patients with nasal eosinophil count > 5 eosinophils per high-power field at nasal cytology had a significantly higher median specific VAS for nasal symptoms and significantly higher SNOT 22 scores.

Conclusions: We demonstrated that blood eosinophil count and nasal cytology may represent useful tools in routine clinical practice to define Type 2 inflammation and that their levels are usually higher in patients with comorbidities. We also showed that blood eosinophilia was not correlated with severity of symptoms, whereas local eosinophil count was associated with high severity of symptoms and high burden on quality of life.

Keywords: SNOT-22; allergic rhinitis; asthma; chronic rhinosinusitis; nasal polyposis.

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