OBJECTIVES. To review the accuracy of fine-needle aspiration cytology in diagnosing non-toxic thyroid nodules and determine what factors are predictive of malignancy in patients with indeterminate cytology results.

DESIGN. Retrospective study.

SETTING. Regional hospital, Hong Kong.

PATIENTS. Patients with non-toxic thyroid nodules undergoing thyroidectomy from December 1999 to December 2003.

MAIN OUTCOME MEASURES. Sensitivity, specificity, positive and negative predictive value of fine-needle aspiration cytology, predictive factors for malignancy in patients with indeterminate fine-needle aspiration cytology results.

RESULTS. The sensitivity, specificity, positive predictive value, and negative predictive value of fine-needle aspiration cytology were 54%, 100%, 100%, and 75% respectively. For the 92 patients with fine-needle aspiration cytology reported as 'indeterminate for malignancy' aspiration cytology subgroup (P=0.005) and age (P=0.001) were significant risk factors for diagnosing malignancy.

CONCLUSIONS. Fine-needle aspiration cytology has high positive predictive value for thyroid cancer, enabling us to 'rule-in' malignant lesions with confidence. Among those with indeterminate fine-needle aspiration cytology, atypical cell lesions and age greater than 40 years conferred increased risk of malignancy.

Key words: Biopsy, needle; Frozen sections; Predictive value of tests; Thyroid nodule

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