title: Determinants of the serum concentration of 1,25-dihydroxyvitamin D in primary hyperparathyroidism.
abstract: 1. The serum concentrations of 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D were measured in 44 patients with primary hyperparathyroidism. 2. In 14 patients the serum concentration of 1,25-dihydroxyvitamin D was greater than normal (142-337 pmol/l). One patient had a subnormal concentration of 1,25-dihydroxyvitamin D (36 pmol/l) but no other evidence of vitamin D deficiency. 3. The possible biological determinants of the serum concentration of 1,25-dihydroxyvitamin D were sought by multivariate analysis of relevant variables. The serum concentration of 1,25-dihydroxyvitamin D was found to be significantly and positively correlated with the serum concentrations of 25-hydroxyvitamin D (P less than 0.001) and parathyroid hormone (P less than 0.003), and with the glomerular filtration rate (P less than 0.03), and negatively correlated with the serum concentrations of calcium (P less than 0.02) and phosphate (P = 0.055) (multiple R = 0.638, P less than 0.002). 4. In primary hyperparathyroidism the major determinant of serum 1,25-dihydroxyvitamin D is the availability of precursor 25-hydroxyvitamin D. 5. The finding that serum 1,25-dihydroxyvitamin D is commonly normal in patients with primary hyperparathyroidism despite an adequate state of vitamin D nutrition, can be explained in terms of the constraining influences of hypercalcaemia and variable degrees of renal dysfunction on the biosynthesis of 1,25-dihydroxyvitamin D.
authors.affiliation: University Department of Medicine, Royal Infirmary, Manchester, U.K.
authors.forename: B C
authors.initials: BC
authors.lastname: Lalor
authors.forename: E B
authors.initials: EB
authors.lastname: Mawer
authors.forename: M
authors.initials: M
authors.lastname: Davies
authors.forename: G A
authors.initials: GA
authors.lastname: Lumb
authors.forename: L
authors.initials: L
authors.lastname: Hunt
authors.forename: P H
authors.initials: PH
authors.lastname: Adams
mesh_terms: D000328:Adult; D000368:Aged; D002112:Calcifediol / Q000097:blood; D002117:Calcitriol / Q000097:blood*; D002118:Calcium / Q000097:blood; D000242:Cyclic AMP / Q000097:blood; D005260:Female; D005919:Glomerular Filtration Rate; D006801:Humans; D006961:Hyperparathyroidism / Q000097:blood* / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D010281:Parathyroid Hormone / Q000097:blood
chemical_list: D010281:Parathyroid Hormone; D000242:Cyclic AMP; D002117:Calcitriol; D002112:Calcifediol; D002118:Calcium