VITAMIN D-BINDING PROTEIN LEVELS IN FEMALE PATIENTS WITH PRIMARY HYPERPARATHYROIDISM

Objective: To determine whether low levels of vitamin D-binding protein (DBP) are related to 25-hydroxyvitamin D (25[OH] D) deficiency in female patients with primary hyperparathyroidism (PHPT). Methods: Twenty-five female patients with PHPT (serum calcium level >10.2 mg/dL and intact parathyroid hormone (iPTH) level >66 pg/mL) and 25 healthy age-and body mass index-matched female control subjects were xaminod. Serum calcium and iPTH levels were determined by commercial laboratories. Levels of 25(OH) D and 1,25-dihydroxyvitamin D (1,25[OH](2)D) were determined by radioimmunoassay, and DBP level was determined by enzyme-linked immunosorbent assay. Results: Serum iPTH and calcium levels were higher in PHPT patients than control subjects (P<.001). Levels of 25(OH) D, albumin, and DBP were lower in the serum of PHPT patients than control subjects (P<.01). There were no significant differences in 1,25(OH) 2D and free 25(OH) D levels between PHPT patients and control subjects. DBP level was inversely correlated with calcium (r = -0.47; P<.01) and iPTH (r = -0.31; P<.05) levels. The 25(OH) D level correlated positively with both DBP (r = 0.28; P<.05) and albumin (r = 0.44; P<.05) levels. Conclusion: Both serum 25(OH) D and DBP levels were lower in female patients with PHPT compared with control subjects. We suggest that a low DBP level contributes to the low 25(OH) D level observed in female PHPT patients. The etiology of the decrease in DBP and its relationship to calcium, 25(OH) D, and PTH levels require further investigation.