Abstract
A simple technique for measuring urine calcitonin (CT) was established using a sensitive radioimmunoassay (RIA) system for plasma human calcitonin (hCT). To extract urinary CT, urine samples were fractioned by gel chromatography on a column (0.8×20cm) of Bio Gel P-2. Recovery of synthetic (1-32) hCT was 86.1±6.2% and the intra-and inter-assay coefficients of variation in RIA were 5.9 and 8.2%, respectively. Dilution curves of the urinary CT after gel-filtration were parallel with the standard curve. In 11 patients with medullary carcinoma of the thyroid (MCT), the CT levels of the urine (in ng/mg Cr) were 3.4 to 20.8 times higher than those of the plasma (in ng/ml), and a significant positive correlation (r=0.93, P<0.001) was obtained between the urinary and plasma levels of CT in these 11 patients. In 32 normal subjects, the CT levels of the urine (in pg/mg Cr) were only 0.41 to 5.1 times of those of the plasma (in pg/ml), and a weak positive correlation (r=0.408, P<0.05) was obtained between these two levels. However, urinary CT levels in normal subjects apparently reflected a rise in endogenous plasma hCT in response to calcium infusion (4mg/kg B.W. for 1min) and that of exogenous plasma CT when synthetic (1-32) hCT (500μg for 1min)
Following gel filtration on a Bio Gel P-30 1.5×80cm column, larger molecular forms of CT than (1-32) hCT were found in the urine not only patients with MCT but also of normal subjects after infusion of calcium or synthetic (1-32) hCT. was injected intravenously.
It is concluded that measurement of urine CT is useful not only for diagnosis of MCT but also for evaluating CT metabolism in normal subjects.
