This study aimed to measure and compare nasal mucus cystatin SN levels in patients with controlled and uncontrolled chronic rhinosinusitis, and to evaluate its diagnostic performance in distinguishing between these disease states.

A total of 98 CRS patients were prospectively enrolled and evaluated for disease control based on the EPOS criteria. Specimens of nasal mucus and tissue from patients with CRS and 15 healthy controls undergoing surgery for the deviated septum were obtained to measure cystatin SN levels. Disease severity was evaluated using the 22-item Sinonasal Outcome Test (SNOT-22), Questionnaire of Olfactory Disorders Negative Statements (QOD-NS) score, Lund-Kennedy score, Lund-Mackay score, olfactory cleft endoscopy scale (OCES), and olfactory cleft computed tomography (CT) score. Multivariable logistic regression analysis was used to determine the risk factors associated with uncontrolled CRS.

Among the patients with CRS, 42.86% were uncontrolled. Cystatin SN expression in the nasal epithelium was significantly increased among patients with uncontrolled CRS compared to those with controlled CRS and healthy controls (both P < 0.001). Furthermore, the uncontrolled CRS exhibited significantly higher blood eosinophil counts (BEC) ( P = 0.001), SNOT-22 score ( P = 0.001), QOD-NS score ( P = 0.004), Lund-Mackay score ( P = 0.022), OCES ( P = 0.004), and olfactory cleft CT score ( P = 0.012) than controlled CRS. Additionally, mucus cystatin SN levels showed a positive correlation with BEC (R = 0.126, P = 0.012) in patients with CRS. Multivariable logistic regression analysis showed that nasal mucus cystatin SN was identified as an independent predictor of uncontrolled CRS (OR = 1.011, P = 0.028). Mucus cystatin SN levels with a cutoff point greater than 106.050 pg/mL had a superior predictive value for uncontrolled CRS compared to BEC (area under the curve, 0.886 vs. 0.782, P < 0.001).

Mucus cystatin SN levels were highly associated with disease severity in patients with uncontrolled CRS.