Improved diagnostic methods in the follow-up of medullary thyroid carcinoma by highly specific calcitonin measurements

Calcitonin (CT) is an important tumor marker for medullary thyroid carcinom a (MTC). Recent CT assays chiefly recognize the monomeric form of CT (mCT). It was the objective of this study to examine the consequences of the high er specificity of the assay for interpretation of the postoperative CT valu es in MTC patients. The postoperative mCT concentration was measured in 214 patients with diffe rentiated thyroid carcinoma (MTC excepted; non-MTC patients) to determine a reference range of mCT in totally thyroidectomized patients. Monomeric CT was also determined with a two-site chemiluminescence immunoassay (Nichols) in 94 healthy subjects and in 68 MTC patients. The mCT concentrations were below the detection limit; in all examined completely thyroidectomized non -MTC patients. Basal and stimulated mCT values were also below the detectio n limit in 32 of the 68 MTC patients. The biochemical and imaging diagnosis of the latter patients did not give any indication of tumor recurrence. We conclude that completely thyroidectomized patients with non-MTC do not s how any measurable mCT concentrations. In comparison with an unspecific CT- RIA, the more specific mCT determination by immunoluminometric assay permit s a more precise differentiation between postoperative normal and pathologi cal values and an earlier diagnosis of recurrent MTC.