Plasma human calcitonin (hCT) levels in normal and pathologic conditions, and their responses to short calcium or tetragastrin infusion.

Plasma hCT levels were less than 50 pg/ml in 50 normal subjects. In 16 patients with medullary carcinoma of the thyroid (MCT), plasma hCT levels were distinctively elevated and they fell significantly after total thyroidectomy, but in 11 of them plasma levels were still high, indicating the presence of metastases. In 74 patients with the other types of malignancy, plasma hCT levels were found to be high in 9 cases (3 oat cell carcinoma of the lung, 4 malignant carcinoids, one malignant pheochromocytoma and one acute myelocytic leukemia). Except for the leukemic case, all these tumors were derived from neural crest. In 12 patients with primary hyperparathyroidism, plasma hCT levels were less than 20 pg/ml. In 13 hypoparathyroid patients, two with pseudohypoparathyroidism and one with pseudoidiopathic hypoparathyroidism, plasma hCT levels were slightly elevated. Some patients with uremia had elevated plasma hCT levels, but there was no relation between plasma levels of hCT and those of PTH, urea nitrogen or creatinine. In response to Ca (4.5 mg/kg/10 min) or tetragastrin (4 mug/kg/5 min) infusion, a marked increase in plasma hCT was observed in all patients with MCT, but not in normal subjects. In 5 hypoparathyroid patients, a significant increase to both stimuli was also observed in all cases. Two patients with pseudopseudohypoparathyroidism responded to the Ca load. These results indicate that the determination of plasma hCT levels especially after a short Ca or tetragastrin infusion is important to study various pathological conditions.