Objective: To evaluate the risk of papillary thyroid carcinoma (PTC) at fine-needle aspiration (FNA) cytology in 34 120 patients.
Results: False positive and false negative rates of FNA cytology were 1.2 and 1.8% in comparison with the histology in 3406 nodules from 3004 patients who underwent surgery. PTC (901 cases) was more frequent in solitary nodule (SN; 446/13 549, 3.3%) than in multinodular goiter (MNG; 411/19 923, 2%, chi(2)=48.8; P<0.0001), and in males (209/6382, 3.3%) than in females (648/26 945, 2.40%, chi(2)=15.58; P<0.0001). PTC prevalence in Graves' disease (GD; 13/286, 4.5%) and Hashimoto's thyroiditis (HT; 31/508, 6.1%) was higher than in SN, this difference being significant in HT (chi(2)=8.7; P=0.003), but not in GD (chi(2)=1.6; P=0.2). Using the multiple logistic regression analysis, independent risk predictors of PTC were determined, which were younger age (odds ratio (OR)=0.97, confidence interval (CI) 0.964-0.974; P<0.0001), male gender (OR=1.44, CI 1.231-1.683; P<0.0001), and SN versus MNG (OR=0.63, CI 0.547-0.717; P<0.0001). The individual risk predictivity was highly improved by including serum TSH in the prediction model, which was measured at FNA in 11 919 patients.
Conclusion: A cytology suspicious or indicative of PTC was associated with younger age, male gender, and solitary versus multiple nodularity. These clinical parameters, together with serum TSH, may allow formulation of an algorithm that could be usefully applied to predict the risk of PTC in individual patients when cytology does not give a diagnostic result.