Low 25‐Hydroxyvitamin D in Primary Hyperparathyroidism: Enhanced Conversion Into 1,25‐Hydroxyvitamin D May Not Be “True” Deficiency

Abstract

Vitamin D deficiency is reported in individuals with primary hyperparathyroidism (PHP). However, decreased 25OHD may be attributed to enhanced conversion into 1,25-hydroxyvitamin D [1,25(OH)D]. To examine vitamin D metabolism in individuals with PHP, serum calcium, PTH, 25OHD, and 1,25(OH)D levels were determined in 210 adults: 102 with PHP, 40 with normal 25OHD, and 68 with vitamin D deficiency. Concentrations were redetermined in 37 individuals with PHP following vitamin D supplementation and 43 patients postsurgery. Comparisons were conducted by Student's t test and ANOVA. Correlations were assessed between PTH and 25OHD, 1,25(OH)D, and 1,25(OH)D/25OHD in individuals with PHP. Calcium, PTH, and 1,25(OH)D were higher (p < 0.001) in individuals with PHP (11.4 AE 0.4, 116 AE 21, 79 AE 6) than in individuals with normal 25OHD (9.6 AE 0.2, 49 AE 5, 57 AE 6) and vitamin D deficiency (9.3 AE 0.2, 62 AE 6, 32 AE 4). Compared with individuals with normal 25OHD (47 AE 5), 25OHD was lower (18 AE 3), but not different from subjects with vitamin D deficiency (15 AE 2). In individuals with PHP, vitamin D2 supplementation induced rises in 1,25(OH)D and calcium without lowering PTH, whereas postsurgery, calcium, PTH, 25OHD, and 1,25(OH)D normalized. Finally, in individuals with PHP, significant correlations (p < 0.01) were documented between PTH and calcium (r = 0.74), 25OHD (r = −0.43), 1,25 (OH)D (r = 0.52), and 1,25(OH)D/25OHD (r = 0.46); and between 1,25(OH)D/25OHD and calcium (r = 0.47). Subnormal 25OHD in most individuals with PHP may be attributed to enhanced conversion to 1,25(OH)D-not "true" vitamin D deficiency-although in some patients, both PHP and vitamin D deficiency coexisted. Moreover, vitamin D supplementation exaggerated hypercalcemia in individuals with PHP.

Concurrent Primary Hyperparathyroidism and Sarcoidosis in a Patient With Severe Hypercalcemia

“…While isolated PHPT is associated with high PTH, the concurrent presence of a PTH-independent etiology could explain the unusually normal PTH concentration observed in our patient. Furthermore, the presence of a low vitamin D despite normal PTH levels further raises the suspicion of a dual pathology of hypercalcemia, as low vitamin D levels are often associated with more severe PHPT, characterized by higher PTH levels [ 14 ].…”