SAT-395 Correlations Between Biochemical Parameters and Trabecular Bone Score (TBS) in Primary Hyperparathyroidism (PHP) Patients

Background: Vitamin D deficiency is common among PHP patients. While data are limited, some studies suggest that vitamin D deficiency may exacerbates skeletal disease in PHP. TBS is a software-based method for assessment of trabecular bone structure of the spine, based on analysis of pixels obtained in dual energy x-ray absorptiometry (DXA) images. The aim of this study was to evaluate TBS, vitamin D status, clinical and laboratorial measurements in a PHP group of patients in a search for a more accurate bone fragility test for risk assessment in this group of patients. Methods: From June/2017 to January/2019, patients who met the criteria for PHP diagnosis were included in this study. Control group was composed by age and sex-matched healthy individuals. Overall, 64 PHP and 63 controls were enrolled. Bone mineral density (BMD) measured by DXA (Hologic QDR 4500) at the lumbar spine, total hip, femoral neck, and TBS values (InSight™) were determined in both groups. Total and ionized calcium, PTH, 25-hydroxyvitamin D (25(OH)D), creatinine, alkaline phosphatase, P1NP and CTX were measured. None were in use of Vitamin D supplementation. Results: As expected, PHP patients had lower BMD values than controls in all sites (p<0.0001). TBS measurements were also reduced in PHP patients compared to controls (1233 vs 1280, p=0.0444). TBS values were inversely correlated with total calcium (CaT) and phosphorus measurements were positively correlated in the PHP patients. 25(OH)D measurements didn’t differ between groups (PHP 22.5 vs. controls 19.8 ng/mL, p=0.1699). There was a positive correlation between 25(OH)D and TBS in both PHP and controls (r= 0,3088, p= 0,0138 and r= 0,3708, p= 0,003 respectively). Considering individuals with vitamin D deficiency (25(OH)D levels <=20 ng/mL), a negative correlation between TBS and CaT measurements among PHP patients (r= -0,4391, p=0,0172) was observeed, while in controls there was a positive correlation between TBS and 25(OH)D (r= 0,3504, p= 0,0362). Conclusion: Serum total calcium presents negative correlation and phosphorus a positive one with TBS in PHP patients. We also found a correlation between TBS and 25(OH)D, both in PHP and in controls. 25(OH)D <=20 ng/mL is an independent risk factor determining degraded TBS among PHP patients and controls.