In numbers of patients with medullary carcinoma of the thyroid (especially those with familial medullary carcinoma of thyroid) the baseline calcitonin may be normal; however, an abnormally large calcitonin response may follow provoca- tive infusion of calcium and/or pentagastrin.[4] (Usually 3-20 times baseline) Most subjects with microscopic medullary carcinoma and all with C-cell hyperplasia have normal basal calcitonin levels;provacative testing is needed. Occasional spurious high results are encountered. Hemolysis can cause spurious high levels. Calcitonin in patient's sera lacks immunoreactive uniformity. Calcitonin is not a screening test.

Patient should be fasting.