Enhanced production rate of 1,25-dihydroxyvitamin D in sarcoidosis

We determined the metabolic clearance and production rates of 1,25-dihydroxyvitamin D [1,25-(OH)2D] in 5 patients with sarcoidosis who had either hypercalciuria or hypercalcemia to examine whether abnormalities in the metabolism of this hormone existed. The mean MCR in the 5 patients with sarcoidosis [40 +/- 9 (+/- SD) mL/min] was similar to that in 13 normal subjects (37 +/- 6 mL/min) and that in 9 patients with absorptive hypercalciuria and renal stones (35 +/- 4 mL/min). However, the mean serum 1,25-(OH)2D concentration was significantly higher in the patients with sarcoidosis (211 +/- 60 pmol/L) than in either of the other 2 groups. The mean 1,25-(OH)2D production rate was markedly elevated in the patients with sarcoidosis (12.4 +/- 5.3 mumol/day), being more than 2-fold greater than the normal mean value (5.4 +/- 1.2 mumol/day). The highest production rates were found in patients with hypercalcemia, whereas subjects with hypercalciuria had production rates comparable to those in the patients with absorptive hypercalciuria. These data indicate that there is no impairment in the clearance of 1,25-(OH)2D in patients with sarcoidosis and that the elevated serum 1,25-(OH)2D levels are due to an increase in its production rate.