American Board of Internal Medicine (ABIM) Certification Practice Exam

What is the minimum size for a thyroid nodule to warrant a biopsy?

1. 0.5 cm

2. 1 cm

3. 1.5 cm

4. 2 cm

The correct answer is: 1 cm

A thyroid nodule generally warrants a biopsy when it reaches a size of 1 cm or greater. This threshold is recommended based on guidelines that balance the risk of malignancy with the practicality of performing biopsies. Nodules that are smaller than this size are typically less likely to be cancerous, and monitoring them is often the preferred approach unless other concerning features (such as suspicious ultrasound characteristics or significant family history of thyroid cancer) are present. In clinical practice, nodules measuring 1 cm or larger are more frequently evaluated with fine needle aspiration biopsy because data indicate that the likelihood of finding a malignancy increases at this size. For example, nodules that measure 1 cm or greater show a higher incidence of thyroid carcinoma compared to those measuring 0.5 cm or smaller, which can usually be observed with regular follow-up unless they exhibit other risk factors. Thus, the minimum recommendation for thyroid nodule biopsy is set at 1 cm to ensure timely identification and intervention for potential thyroid malignancies.