Total, Free and Bioavailble 25 OH D and Bone Disease in Primary Hyperparathyroidism

Background: Low levels of vitamin D 25OHD are frequently described in PHP patients. The aim of this study was to evaluate bone parameters and vitamin D status in PHP patients and controls. Methods: Prior to surgery, 64 PHP patients and 63 healthy matched control subjects regarding age, gender and body mass index were enrolled in this study along 18 months. 25OHD and PTH were measured using Roche® Immunoassays. Bone mineral density (BMD) by dual X-ray absorptiometry (DXA) (Hologic QDR 4500) and TBS (InSight™) were determined in all patients and controls. Distribution of total, bioavailable and free (calculated) 25OH and its correlation with TBS and DXA in both groups was evaluated. DBP (vitamin D binding protein) SNPs genetic analysis was performed by ABI 7500 real time PCR System. None of the patients and controls were taking vitamin D supplements before the study. Results: PHP patients had lower BMD values than controls in all sites (p<0.01). TBS measurements were also reduced in PHP patients compared to controls, as expected (1233 vs 1280, p=0.04). There was no statistical difference in free, total and bioavailable 25OHD measurements between the PHP and the control group, mean±SD: 3.4±1.7 vs 3.1±1.7 pg/mL (p=0.44), 22.6± 6.1 vs 20.6± ng/dL (p=0.13) 1.53±0.66 vs 1.41±0.61 ng/mL (p=0.28), respectively. Likewise, there was no statistical difference in DBP haplotypes 1s/1s, 1f/1f, 1s/1f, 2/2, 1s/2, 1f/2 analysis between groups. There was no correlation with 25OHD and DXA measurements in both groups. However, total 25OHD presented statistical significant correlation with TBS measurements in the PHP group (r=0.28; p=0.02) and total, free and bioavailable 25OHD measurements with TBS in the control group (r=0.42; r=0.42; r=0.43; p<0.01). Conclusion: Vitamin D status correlates with TBS, but not with DXA, highlighting the relation of the vitamin D with the microarchitecture bone parameters in both PHP patients and controls. However, this correlation was more evident among controls than in PHP patients, spotlighting the primary hyperparathyroidism effects in bone.