Background Eosinophilic chronic rhinosinusitis (eCRS) is linked with skewed T-helper 2 or immunoglobulin E (IgE)-mediated allergic responses, with differing diagnosis, prognosis, and management to non-eCRS. Objective The association between biomarkers and eCRS was investigated to assess the predictors of eCRS. Methods A cross-sectional study of adult patients with chronic rhinosinusitis (CRS) undergoing endoscopic sinus surgery was conducted. eCRS was defined by histopathological assessment showing >10 eosinophils/high-power field on sinus mucosal biopsy. Blood tests were performed preoperatively and assessed for a full blood count including eosinophils and a white cell count (WCC) as well as biochemical markers of inflammation and atopy including Immunoglobulin E (IgE), C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), and ImmunoCAP testing for serum-specific IgE. Comparisons between eCRS and non-eCRS patients were performed. Results 345 patients (48.1% female, age 48.72 ± 15.06 years) were recruited, with 206 (59.7%) identified as eCRS, 41% with asthma and 47% CRS with nasal polyps. eCRS patients were more likely to have asthma ( P < .01) and nasal polyps ( P < .01). Blood eosinophils were significantly elevated in eCRS (0.42±0.34 vs 0.17±0.13 × 10⁹/L, P < .01) as were eosinophils as a ratio of WCC (6.21 ± 4.48 vs 2.55 ± 1.84, P < .01). ESR was decreased when compared with non-eCRS (8.1±7.87 vs 10.65±11.91, P = .03). Receiver operating characteristic curve analysis predicted high tissue eosinophilia at blood eosinophil levels above 0.24 × 10⁹/L (sensitivity 70.9%, specificity 78.4%, area under the curve [AUC]: 0.792, P < .01). eCRS was predicted at eosinophil above 4.27% of total WCC (sensitivity 64.1%, specificity 88.5%, AUC 0.797; P < .01; positive predictive value 89.2%, negative predictive value 62.4%, positive likelihood ratio 5.57, and diagnostic odds ratio 13.71). There was no significant association among WCC, CRP, IgE, or ImmunoCAP testing. Conclusion eCRS is associated with elevated blood eosinophils (>0.24 × 10⁹/L), eosinophil ratio (>4.27% of total WCC), and lower ESR when compared with non-eCRS.

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