Predictive value of serum calcitonin levels for preoperative diagnosis of medullary thyroid carcinoma in a cohort of 5817 consecutive patients with thyroid nodules

Context: Routine serum calcitonin (CT) measurement in patientswith thyroid nodules for diagnosis of medullary thyroid carcinoma(MTC) is controversial.Objective: The objective of this study was to evaluate the diagnosticaccuracy of systematic CT measurement in non-multiple endocrineneoplasia type 2 patients with nodular thyroid disease.Settings: This study was conducted at a national healthcare systemhospital (outpatient and inpatient sectors).Subjects: Consecutive patients with nodular thyroid disease (n 5817) were studied.Main Outcome Measures: Serum CT levels were measured underbasal conditions, and when basal values were more than or equal to20 and less than 100 pg/ml, testing was repeated after pentagastrinstimulation. Basal or stimulated levels more than 100 pg/ml wereindication for surgery.Results: Fifteen cases of MTC and seven of C cell hyperplasia (CCH)were identified. MTCs were diagnosed in all patients with basal CTmore than 100 pg/ml. The four patients with basal CT more than orequal to 50 and less than 100 pg/ml included two diagnosed with MTCand two with CCH. In 10 patients with basal levels more than or equalto 20 and less than 50 pg/ml, histology confirmed the presence of MTCin four, four others had CCH, and the remaining two were negativefor thyroid malignancy. Positive predictive values for basal CT levelsin the preoperative diagnosis of MTC were: 23.1% for values morethan or equal to 20 pg/ml, 100% for values more than 100 pg/ml, 25%for levels more than or equal to 50 and less than 100 pg/ml, and 8.3%for values more than or equal to 20 and less than 50 pg/ml. Positivepredictive values for the pentagastrin test (100 pg/ml) were 40% inthe entire series.Conclusions: CT screening of thyroid nodules is a highly sensitivetest for early diagnosis of MTC, but confirmatory stimulation testingis necessary in most cases to identify true positive increases. (J Clin