The detection of elevated plasma levels of carcinoembryonic antigen in patients with suspected or established medullary thyroid carcinoma.

Plasma levels of carcinoembryonic antigen (CEA) and calcitonin (CT) were measured in 35 normal control subjects and in 37 patients with suspected or established medullary thyroid carcinoma (MTC). None of the normal control subjects had elevated basal plasma levels of either CEA (greater than 5 ng/ml) or CT (greater than 0.25 ng/ml). However, of the 37 patients with suspected or established MTC, 23 (62%) had elevated basal plasma levels of CEA (range 9.8--7,000 ng/ml) and 27 (73%) had elevated basal plasma CT values (range 0.30--500 ng/ml). Generally, patients with clinically apparent MTC, either primary or metastatic, had higher plasma CEA and CT levels than those with occult disease. A positive correlation was found (r = 0.785, p less than 0.01) when comparing basal plasma CEA and stimulated plasma CT levels in 20 patients. A marked increase above the basal plasma level of CT but not CEA was detected in each of six MTC patients following intravenous calcium or pentagastrin. These data demonstrate that basal plasma levels of CEA and CT were increased in a large percentage of patients with MTC. Plasma calcitonin levels unlike plasma CEA levels were more often elevated in patients with occult disease and were increased above basal following the intravenous administration of either calcium gluconate or pentagastrin.