Background: The American College of Radiology (ACR) TI-RADS 2017 guidelines recommend size-based thresholds for biopsy of thyroid nodules, aiming to improve diagnostic accuracy while minimizing unnecessary procedures. However, the validity of these criteria in real-world clinical settings, particularly in India where the incidence of differentiated thyroid cancer (DTC) is rising, remains underexplored.

Objective: To evaluate the diagnostic performance of ACR TI-RADS 2017 size-based biopsy recommendations in identifying thyroid malignancy.

Methods: A prospective study was conducted at Government Medical College, Thiruvananthapuram, including 240 thyroid nodules from 162 patients over a period of 1.5 years. All nodules >1 cm or TIRADS 4/5 nodules >5 mm underwent ultrasound-guided FNAC. Nodules with Bethesda categories 4–6 underwent surgery; Bethesda 3 nodules were either followed up or surgically excised based on patient preference. Final outcomes were based on cytology (Bethesda 2) or histopathology.

Results: Of the 226 nodules with definitive outcomes, the malignancy rate was 11.5%. The ACR TI-RADS size criteria demonstrated a sensitivity of 92.85% and specificity of 63.07% in detecting malignancy. Among biopsies performed as per ACR size recommendations, 15.29% were malignant. Only 1 out of 124 nodules not meeting biopsy criteria was malignant (0.8%).

Conclusion: The ACR TI-RADS 2017 size-based biopsy thresholds exhibit high sensitivity and moderate specificity, effectively minimizing missed malignancies while avoiding a large number of unnecessary FNACs. However, a small risk of missing cancers persists, raising the need to re-evaluate the size criteria, especially for nodules with high-risk sonographic features. Larger multicenter studies are essential to optimize these thresholds for enhanced diagnostic precision