Calcitonin screening in patients with thyroid nodules

Objectives To validate the positive predictive value (PPV) of a slightly elevated basal calcitonin (CT) for the diagnosis of medullary thyroid cancer (MTC) in a center for thyroid disorders.

Methods A total of 11,270 patients with thyroid nodules underwent calcitonin screening successively in an outpatient clinic of the university. Patients with known elevation of CT, renal insufficiency, bacterial infection, alcohol abuse, proton-pump inhibitor therapy or autoimmune thyroid disease were excluded from further analysis. Serum CT levels were determined using Immulite 2000. If possible, a pentagastrin test was done to differentiate cases of hypercalcitoninemia.

Results Hypercalcitoninemia (CT≥13 pg/ml) was found in 32 patients. Urgency of surgery was adjusted according to the degree of hypercalcitoninaemia and/or stimulated CT, gender and sonographic and scintigraphic appearance of the thyroid nodules. In consequence, 20 of 32 CT-positive patients underwent surgery and in 10 of the operated patients an MTC was confirmed histopathologically. Thus, the PPV of hypercalcitoninemia for MTC was calculated with 31 % (n=10/32). The PPV increased to 50 % for those patients who underwent surgery (n=10/20). In 6 patients with clearly elevated CT-levels (>50 pg/ml) an MTC was detected surgically in all cases. In contrast, in 14 patients with slightly elevated levels of basal CT (13 - 50 pg/ml) surgery revealed evidence of MTC only in 4 cases. This resulted in a PPV of only 15 % (n=4/26) in cases with slightly elevated basal CT; although the value increased to 28 % when only surgically treated patients were considered (n=4/14).

Conclusions Taking all clinical data into account, calcitonin screening has an acceptable PPV for medullary thyroid cancer in patients with thyroid nodules. With respect to the relatively low cost and non-invasive nature of the test, the systematic performance of calcitonin screening can be advocated in centers for thyroid disorders, despite the overall low prevalence of MTC.