Relevance of vitamin D metabolite concentrations in supporting the diagnosis of primary hyperparathyroidism.

We compared the relationships between 25-hydroxyvitamin D [25(OH)D] and 1,25-dihydroxyvitamin D [1,25(OH)2D] levels in patients with primary hyperparathyroidism (PHPT) and 38 volunteer blood donors. There was no significant difference in mean 25(OH)D levels between patients with PHPT (34 +/- 21 nmol/L; n = 21) and the donor samples (41 +/- 19 nmol/L; n = 38). Serum 1,25(OH)2D levels were higher in the patients with PHPT compared with the donors (122 +/- 61 pmol/L vs 56 +/- 41 pmol/L; p less than 0.001). The 95th percentile 1,25(OH)2D value for the donors was exceeded in 65% of the patients with PHPT. There was a significant correlation between serum 1,25(OH)2D versus 25(OH)D in the patients with PHPT (r = 0.50; p less than 0.05) but not in the donors (r = 0.02). We conclude from the distinct elevation in 1,25(OH)2D levels in the majority of our patients with PHPT that the concentration of this parathyroid hormone-dependent hormone can be of critical value in corroborating the diagnosis of PHPT.