Negative predictive value of procalcitonin in medullary thyroid carcinoma

Calcitonin (CT), the major biochemical marker in medullary thyroid carcinoma (MTC) is prone to in vitro instability and suffers from scarcity of clinical laboratory platforms. Procalcitonin (PCT), the precursor of CT, free of these shortcomings, has been reported as a potential MTC marker. The aim of this study was to assess the negative predictive value (NPV) of PCT as a first-line marker in MTC. 476 serum samples referred to our laboratory for CT measurements were analyzed for PCT. NPVs of PCT were assessed at 3 cut-offs (0.05, 0.10 and 0.15 ng/mL) and the diagnosis of MTC was based on CT levels. PCT and CT levels were correlated (r=0.7554 for CT levels above 10 pg/mL, n=66). Accepting the CT cut-off based on the upper reference limit the NPV of PCT were 98.1% (0.05 ng/mL), 96.3% (0.10 ng/mL) and 95.4% (0.15 ng/mL) respectively. For a CT cut-off of 100 pg/mL the NPVs of PCT were 100% for all PCT thresholds. Serum PCT has a strong NPV and could be a good candidate for a first-line screening test to exclude MTC in patients with suspicious thyroid nodules or suggestive symptoms. Larger prospective studies are necessary to confirm our results.