Clinical evaluation of ECP in patients with rhinitis

Objective: This study aimed to evaluate the diagnostic performance of serum ECP levels in differentiating rhinitis subtypes SAR, PAR and NARES in adult patients. A specific focus was placed on whether serum ECP could serve as a viable alternative to nasal cytology, which is often operator-dependent and may be uncomfortable for the patient. Methods: This retrospective study included 484 patients presented to the Allergy Outpatient Clinic between 2019 and 2023. Patients were classified as SAR (n=59), PAR (n=228), or NARES (n=197). Serum ECP levels, nasal cytology results, and gender were analyzed. Results: Serum ECP levels differed significantly among the three groups (p<0.001). The highest ECP levels were observed in the SAR group (median: 41 ng/mL), followed by NARES (36 ng/mL), and the lowest in PAR (26.5 ng/mL). Notably, 90.4% of NARES patients had ECP levels ≥24 ng/mL. Pairwise comparisons showed significant differences between PAR and both SAR (p=0.049) and NARES (p<0.001), whereas no significant difference was found between SAR and NARES (p=1.000). Conclusion:Serum ECP level serves as a significant biomarker, particularly in differentiating between NARES and PAR groups. However, the data obtained in the present study suggest that ECP has the potential to replace nasal cytology in the diagnosis of NARES. Nonetheless, it is recommended that ECP levels and nasal cytology findings be evaluated together in clinical practice. With future prospective and long-term studies, serum ECP may hold the potential to become the gold standard in the diagnosis of NARES. Keywords: Eosinophilic cationic protein, allergic rhinitis, NARES, nasal cytology, eosinophilia