Elderly age and male gender as risk factors for Non Diagnostic cytology at thyroid fine needle aspiration: results of a large cytological series

Non-diagnostic (ND) result of ultrasound-guided fine-needle aspiration cytology (FNAC) of thyroid nodules can lead to diagnostic delays, repeated procedures and, potentially, unnecessary surgeries. This study aimed to evaluate the role of patient age and gender as predictors of a ND cytological result of FNAC, both at first sampling and after repeat procedures. We retrospectively analyzed 5,774 FNACs performed between October 2017 and April 2025 at a single tertiary center. All procedures were conducted by an experienced endocrinologist and interpreted by a single expert cytopathologist. ND rates were compared by age and gender. Logistic regression assessed independent associations, and interaction analysis evaluated whether age effects differed by gender. ND cytology occurred in 29.5% of cases. Patients with ND results were older (59.3 ± 14.2 vs. 57.3 ± 14.0 years, p < 0.001) and more often male (29.6% vs. 23.0%, p < 0.001). Logistic regression confirmed male gender (OR 1.376, 95% CI 1.211–1.563) and age (OR 1.009, 95% CI 1.005–1.013) as independent predictors (p < 0.001 for both), with a significant age × gender interaction (p = 0.036), showing a stronger age effect in males. Among 443 patients repeating FNAC after an initial ND result, 39% remained ND, with no significant age or gender differences between persistent-ND and diagnostic outcomes. Elderly age and male gender independently increase the likelihood of ND FNAC results. These factors should be considered when planning thyroid FNAC, although they do not predict persistent ND outcomes upon repeat sampling.