After a nondiagnostic (ND) result or findings of atypia of undetermined significance/follicular lesion of undetermined significance (AUS/FLUS), the current recommendation is for fine-needle aspiration cytology (FNAC) of the thyroid nodule to be repeated after at least 3 months. The aim of this study was to evaluate whether the interval between FNACs has any influence on the final cytological diagnosis.

This was a retrospective study including all patients who underwent FNAC for the first time between January 2016 and December 2019 with ND or AUS/FLUS cytological results and then underwent a second FNAC procedure. Demographic, clinical, ultrasound and cytological data were retrieved. 1,497 nodules were evaluated; 535 had a first FNAC result of ND or AUS/FLUS, and 246 of these were re-evaluated with a second FNAC. The cases were grouped according to the timing of the repeat FNAC in two different analyses: < vs. ≥ 3 months and < vs. ≥ 6 months after initial FNAC.

Two hundred forty-six repeat FNACs were performed in 186 patients (76% female, median age 59.5 years). Twenty-two of these procedures (8.9%) were performed within 3 months, and 115 (46.2%) within 6 months of the first FNAC. Second FNAC findings were ND in 121 (49.2%) cases, benign in 103 (41.9%), AUS/FLUS in 8 (3.3%), follicular neoplasm/suspicious follicular neoplasm in 9 (3.7%), suspicious malignancy in 4 (1.6%) and malignancy in 1 (0.4%). Early repetition of FNAC did not significantly influence the final cytological result (< 3 vs. ≥ 3 months, P=0.51; and <6 vs. ≥ 6 months, P=0.20).

This study suggests that the interval in repeat FNAC procedures is not relevant to overall diagnostic performance.