Purpose: To evaluate total and free vitamin D metabolites and hormone-to-prohormone [1,25(OH)2D/25(OH)D] “activation ratio” in PHPT patients with low or insufficient vitamin D status. Methods: Thirty female patients with primary hyperparathyroidism (PHPT) and 30 age and body mass index (BMI) matched healthy controls were enrolled. Serum levels of calcium, intact parathyroid hormone (iPTH), vitamin D binding protein (DBP), albumin, total 25(OH)D and 1,25(OH)2D were measured. The activation ratio of vitamin D was calculated as total 1,25(OH)2D/25(OH)D. Calculated serum-free 25(OH)D and 1,25(OH)2D levels were also reported. Results: Compared to the control subject, patients with PHPT had a lower total 25(OH)D and DBP levels (p < 0.001). The serum concentration of free 25(OH)D and total 1,25(OH)2D were similar between the two groups; but free 1,25(OH)2D levels were about 26% higher in the PHPT patients compared to controls (p < 0.001). PHPT patients had a significantly higher activation ratio (p < 0.01), although their total 25(OH)D were lower than controls. The free (but not total) 1,25(OH)2D level was inversely correlated with DBP (p < 0.01). Both free 1,25(OH)2D levels and activation ratio were positively correlated with iPTH and calcium levels (p < 0.01). The activation ratio was highly correlated with levels of total vitamin D stores and free vitamin D metabolites (p < 0.001). Conclusion: Patients with PHPT had significantly higher free 1,25(OH)2D levels and activation ratio compared to control subjects. We suggest that levels of free vitamin D metabolites and vitamin D activation ratio may provide additional values for the diagnosis and therapeutic choices in these patient populations with compromised vitamin D status.
All Science Journal Classification (ASJC) codes
- Endocrinology, Diabetes and Metabolism
- 1,25-Dihydroxyvitamin D
- Parathyroid hormone
- Vitamin D
- Vitamin D activation ratio