What Are the Keys to Successful Thyroid FNA Interpretation?
Ultrasonography (US) has had a significant impact on TFNAB because it detects nonpalpable nodules, which, without US, would likely go undetected in the patient's lifetime. In a biological system, increasing test sensitivity (detection of thyroid nodules) reduces specificity (ability to distinguish benign from malignant nodules). About 40% of thyroid nodules are currently detected by US and 50% identified at autopsy. The incidence of newly detected thyroid malignancies is <50 000/year in the United States, and roughly 3·6% of those patients will die from their disease. Thus, the more screening by US, the greater the chance patients will undergo TFNAB for a benign condition. This reduces the positive predictive value (PPV) of TFNAB without practically improving its negative predictive value (NPV). The middle two columns in Table 1 show that if the prevalence of malignancy in a patient population is reduced from our 9·3% level to, arbitrarily, 1% because of increased screening, the PPV drops to 13% with no appreciable change in the NPV.
The Utilization of Ultrasonography
Ultrasonography (US) has had a significant impact on TFNAB because it detects nonpalpable nodules, which, without US, would likely go undetected in the patient's lifetime. In a biological system, increasing test sensitivity (detection of thyroid nodules) reduces specificity (ability to distinguish benign from malignant nodules). About 40% of thyroid nodules are currently detected by US and 50% identified at autopsy. The incidence of newly detected thyroid malignancies is <50 000/year in the United States, and roughly 3·6% of those patients will die from their disease. Thus, the more screening by US, the greater the chance patients will undergo TFNAB for a benign condition. This reduces the positive predictive value (PPV) of TFNAB without practically improving its negative predictive value (NPV). The middle two columns in Table 1 show that if the prevalence of malignancy in a patient population is reduced from our 9·3% level to, arbitrarily, 1% because of increased screening, the PPV drops to 13% with no appreciable change in the NPV.
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