A Pilot Study on the Relationship Between Time to Formalin Fixation and Changes in Eosinophil Infiltration in Nasal Polyps

Background Tissue eosinophil counts are commonly used as prognostic markers in chronic rhinosinusitis with nasal polyps (CRSwNP) and to determine eligibility for financial assistance based on established criteria, highlighting an evolving importance. However, no standardized protocols govern specimen handling from collection to formalin fixation yet. This gap in practice is clinically meaningful, as the effect of pre-fixation delay on eosinophil counts and epithelial integrity remains poorly defined. Objective To determine whether time to formalin fixation influences eosinophil counts and epithelial integrity in nasal polyps from patients with CRSwNP. Methods Clinical nasal polyp specimens processed through our institution's standard surgical pathology workflow and a controlled research protocol were evaluated histologically with hematoxylin and eosin staining. For clinical specimens, time from collection to fixation was recorded and eosinophils were enumerated. In the experimental portion, research specimens were sectioned and fixed at 0 h, 1 day, 3 days, and 7 days after excision. Eosinophil counts and epithelial injury scores were compared across time intervals and correlated with fixation delay. Results Time to formalin fixation ranged from 51 min to 19 h, and longer delays correlated with greater eosinophil reduction ( r = −0.867, p = .057). In the experimental portion, eosinophil counts were lower at 1, 3, and 7 days than at 0 h ( p < .05), and fixation time was negatively correlated with eosinophil count ( r = −0.39, p < .05). Epithelial injury scores increased at 1, 3, and 7 days ( p < .05), and positively correlated with fixation time ( r = 0.72, p < .05). Conclusions Delayed formalin fixation reduces eosinophil counts and worsens epithelial preservation in nasal polyps. Standardization of tissue handling and fixation timing may improve the reliability of histologic eosinophil assessment in CRSwNP patients.