Endocrine Abstracts

Introduction: Vitamin D insufficiency is very common among Spanish adults. It is well established there is an inverse relationship between vitamin D and PTH levels. The diagnostic approach of an increased serum PTH concentration in a normocalcemic normophosphatemic patient is frequent in routine practice and the deficiency of vitamin D is the major cause of secondary hyperparathyroidism (SHPT). The aims of this study were to evaluate the prevalence of SHPT in a cohort of normocalcemic patients with elevated serum PTH levels and deficiency/ insufficiency of vitamin D and to analyze the correlation between PTH and vitamin D levels.

Methods: 96 patients with elevated PTH levels and a 25OHD <30 ng/ml were included. All patients were treated with vitamin D for 3–6 months and all parameters were re-evaluated. Patients with diabetes and chronic kidney disease were excluded.

Results: 96 patients were included (61.3% female; 63.22±12.56 median age). Baseline characteristics were: Serum calcium: 9.87±0.93 mg/dl, serum phosphate: 3.08±0.54 mg/dl, calciuria: 180.3±123 mg/dl/24 h, PTH: 117±42 and 25(OH) vitamin D: 14.86±3.3 ng/dl. After treatment with vitamin D there was a significant increase of 25(OH) vitamin D levels (40.36±19, P<0.0001) and a significant decrease of PTH levels (83±40 P<0.001), serum calcium (9.8±0.58, P<0.037), and calciuria (199±123 mg/24 h; P<0.032). 12 patients were diagnosed of primary hyperparathyroidism (12.5%). Plasma 25(OH)D3 levels correlated negatively with PTH levels (r=−0.261, P<0.01). For the diagnosis of hyperparathyroidism in patients with vitamin D levels low 20 ng/ml the threshold of 108.5 pg/ml for PTH levels was obtained by means of the ROC curve analysis, with 87% of sensitivity and 58% specificity.

Conclusions: Vitamin D deficiency/insufficiency is the major cause of secondary hyperparathyroidism. To adequately assess this condition is critical to replenish levels of vitamin D. PTH threshold for hyperparathyrodism diagnosis in vitamin D deficiency must be calculated.