Serum calcitonin estimation in medullary thyroid cancer: basal or stimulated levels?

Calcitonin (Ct) is a tumour marker essential for the diagnosis and follow-up of medullary thyroid cancer (MTC). Accurate and consistent measurements of serum Ct are of critical importance. Ct measurements by different methods can differ, leading to difficulties in the interpretation of results. Second generation assays for Ct have been developed and are now available in clinical laboratories. However, the lack of standardization for Ct assays remains a common problem with Ct assays. The reference interval and reliability should be carefully defined. The role of stimulated Ct for the diagnosis and follow-up of MTC should also be pointed out as the pentagastrin test is no more available in all countries. However, the stimulated test remains very useful to exclude MTC if the basal Ct serum level is in the grey zone (15-20 ng/L), after surgery to confirm the complete cure. A residual response after surgery could indicate a need for aggressive surgery or - in case of metastatic disease - could suggest the prognosis. High-dose Ca test (2.5mg/kg) seems to be a reliable and effective test for the diagnosis and follow-up of MTC. It seems more potent than pentagastrin with fewer side effects. The threshold able to discriminate healthy subjects from C-cell hyperplasia (CCH) cases for the stimulated Ct concentration is 184 ng/L for women and 1620 ng/L for men. As stimulated Ca test will eventually replace the pentagastrin test, there is a need to confirm or to modify the threshold identified for each assay individually.