False-positive, false-negative, and indeterminate fine-needle aspiration (FNA) biopsy results complicate the management of patients with thyroid nodules.

Thyroid FNA results from 240 consecutive patients (seen 1991 to 2002) were categorized into four groups: positive for malignancy, negative for malignancy, indeterminate for malignancy, and nondiagnostic. Indeterminate results included follicular neoplasm, Hürthle cell neoplasm, and suspicious for papillary carcinoma. The FNA results were compared with histopathologic analysis after thyroidectomy.

The FNA results were 76 (32%) positive for malignancy, 53 (22%) negative for malignancy, 100 (42%) indeterminate for malignancy, and 11 (5%) nondiagnostic. There were 3 (4%) false-positive and 2 (4%) false-negative FNA results. Among the 100 indeterminate FNA results, carcinoma was found in 11 (15%) of 73 follicular neoplasms, 2 (20%) of 10 Hürthle cell neoplasms, and 14 (82%) of 17 suspicious for papillary carcinoma. For the 73 patients with follicular neoplasms, nodule diameter >2 cm was associated with an increased risk of malignancy (P <0.03).

False-negative FNA results are uncommon, supporting the practice of observation in most of these patients. Among those with indeterminate biopsy results, high-risk subgroups include patients with FNA results suspicious for papillary carcinoma and follicular neoplasms >2 cm.