The Potential Role of Nasal Cytology in Respiratory Diseases: Clinical Research and Future Perspectives

Nasal cytology is a non-invasive, affordable, and easily executable technique commonly used in research to study rhinitis and, to a lesser extent, chronic rhinosinusitis. It is particularly useful for the differential diagnosis of non-allergic rhinitis and for phenotyping chronic rhinosinusitis. Allergic rhinitis, asthma, and aspirin intolerance are frequent comorbidities of chronic rhinosinusitis. A diagnostic system has been proposed to assess the severity of chronic rhinosinusitis (clinical-cytological grading), incorporating nasal cytology and comorbidity observation. This score correlates with the recurrence risk of chronic rhinosinusitis with nasal polyposis. Specifically, a higher grade is often linked to asthma, aspirin intolerance, a recurrent disease requiring surgery, and a mixed cell phenotype (eosinophilic and mast cell). Although nasal cytology has been shown to be able to replace bronchial analysis with acceptable precision due to its technical characteristics, its use in diseases affecting both upper and lower airways remains limited. The main limitation of this technique is its lack of standardization, which currently hinders its widespread clinical adoption despite its increasing familiarity among allergists and otolaryngologists. In the context of the unitary airways hypothesis, nasal cytology could also provide valuable insights for managing lower airway diseases like chronic obstructive pulmonary disease and obstructive sleep apnea syndrome, which significantly impact quality of life and healthcare costs. This review aims to provide an overview of nasal cytology, highlighting its limitations and potential applications in chronic respiratory diseases.