[How do you investigate an elevated calcitonin level?].

This article describes a case of lung cancer with associated hypercalcitoninemia in a man with a goitre. The case raises the problem of the differential diagnosis between medullary thyroid carcinoma and a neuroendocrine neoplasm with ectopic calcitonin secretion. The article first reviews the physiology of calcitonin, then outlines the diagnostic tests that are required to investigate hypercalcitoninemia and finally discusses the interpretation of test results.