Ionized calcium and 1,25-dihydroxyvitamin D concentration in serum of patients with sarcoidosis

The aim of this study was to evaluate alterations in calcium metabolism in sarcoidosis. The serum concentrations of calcium (sCa), ionized calcium (sCa2+), 1,25-dihydroxyvitamin D (s1,25(OH)2D3) and parathyroid hormone (sPTH), serum angiotensin-converting enzyme activity (sACE) and urinary excretion of calcium (uCa) were studied in 36 Japanese patients with pulmonary sarcoidosis, aged 48.1+/-15.3 yrs (mean+/-SD), 15 males and 21 females. During the study the patients were on a daily diet with 500 mg calcium and 1000 mg phosphorus for a total of 6 days. sCa2+ was above the normal range (>1.26 mmol x L(-1)) in 10 patients (27.8%), 12 patients (33.3%) were hypercalciuric, and 16 patients (44.4%) showed alteration in calcium metabolism, with an increase in values of sCa, sCa2+ or uCa. There was a significant correlation between sCa2+ and s1,25(OH)2D3 (p<0.001), as well as between sCa2+ and sACE (p<0.001). s1,25(OH)2D3 in patients with extrathoracic involvement (ETI) tended to be higher than in patients without ETI. sCa2+ was less than 1.23 mmol x L(-1) (p<0.05) in the majority of patients without ETI, and sCa2+ was less than 1.24 mmol x L(-1) in the majority of normocalciuric patients. In conclusion, a disease-related alteration in calcium metabolism was seen in about 40% of patients with sarcoidosis, and 1,25-dihydroxyvitamin D probably plays a crucial role in this abnormality. The serum concentration of ionized calcium was considered to be a useful index for the disease activity of sarcoidosis.