To identify the factors responsible for cytological failure in diagnosis of small thyroid nodules by ultrasound-guided fine needle aspiration (US-FNA).

A total of 298 patients with small thyroid nodules underwent US-FNA at Bengbu Third People's Hospital from October 2018 to June 2020. Nodules were classified into categories Ⅰ-Ⅵ according to the results of puncture cytology examination, in which class Ⅰ was undiagnostic, and the ultrasonic characteristics of class Ⅰ and classes Ⅱ-Ⅵ nodules were compared. Statistically significant parameters from univariate analysis were included in Logistic multivariate regression to analyze factors responsible for failed diagnosis in US-FNA specimens.

A total of 332 thyroid nodules were included, of which 43 were class Ⅰ nodules, 143 class Ⅱ, 15 class Ⅲ, 11 class Ⅳ, 81 class Ⅴ, and 39 class Ⅵ. Class Ⅰ nodules were undiagnosed ones, accounting for 12.9% (43/332). The univariate analysis demonstrated significant differences in diameter, echo, calcification, and blood supply between class Ⅰ and classes Ⅱ-Ⅵ nodules (P＜0.05). The multivariate Logistic regression analysis demonstrated that nodular diameter ≤0.05 (odds ratio [OR]=6.488, 95% confidence interval [CI]: 2.905-14.491, P＜0.001), low echo (OR=9.027, 95%CI: 1.107-73.582, P=0.040), no blood supply (OR=4.016, 95%CI: 1.226-13.148, P=0.022), and circular calcification (OR=6.458, 95%CI: 1.422-29.331, P=0.016) were independent risk factors for failed diagnosis of US-FNA specimens.

Nodular diameter ≤0.05, low echo, no blood supply, and circular calcification are independent risk factors for failed diagnosis of fine needle puncture specimens.