Introduction: The rates of atypia of undetermined significance (AUS) by fine-needle aspiration (FNA) and malignant outcomes have been estimated at < 7% and 5–15%, respectively. Initial AUS diagnosis is followed up clinically with serial ultrasounds, repeat FNA, molecular testing, or direct surgery. We investigated the incidence, follow-up modalities, and final outcomes of AUS in Newfoundland. Methods: All cases of AUS diagnosed at the Eastern Health Cytology Laboratory between 1 January 2010 and 31 December 2013 were identified. Electronic medical records were examined for follow-up modalities and final histologic diagnosis. The final outcomes were reported as benign, malignant, or undetermined. Results: Out of 3,285 thyroid FNAs, 181 (5.5%) were AUS. Fifty-seven (31.5%) had repeat FNA diagnosed as benign (38.6%), AUS (29.8%), or suspicious/malignant (8.8%). Eighty-four (46.4%) had surgery after the first AUS diagnosis, 39 (46.4%) of which were malignant. Twenty-four patients (13.3%) were followed up by serial ultrasound only, 2 (1.1%) by molecular testing, and 1 (0.6%) died of unrelated disease. Thirteen (7.2%) had no follow-up record. Our malignancy rate (MR) was 29.8%. Conclusion: The MR in our population was higher than the rate proposed by The Bethesda System for Reporting Thyroid Cytopathology. Repeat FNA can reduce the rate of unnecessary surgeries, but practice guidelines should consider individual and institutional circumstances. The ratio MR:ADR (AUS diagnostic rate) may be a better indicator of performance.

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