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Vitamin D, 1,25-Dihydroxy (Serum)

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1,25-Dihydroxyvitamin D (calcitriol) is the active hormonal form of vitamin D. During pregnancy, circulating levels rise substantially due to increased renal and placental 1α-hydroxylase activity, especially in the 2nd–3rd trimesters.

Units Non-pregnant Adult 1st Trimester 2nd Trimester 3rd Trimester
pg/mL 25 – 45 20 – 65 72 – 160 60 – 119
pmol/L 60 – 108 52 – 169 187 – 416 156 – 309
Causes of High 1,25-Dihydroxyvitamin D
  • Pregnancy (physiologic rise)
  • Primary hyperparathyroidism
  • Sarcoidosis and other granulomatous diseases (↑ extrarenal activation)
  • Vitamin D intoxication
  • Lymphoma
  • Idiopathic hypercalcemia syndromes
  • Renal hyperfiltration or increased 1α-hydroxylase activity
Causes of Low 1,25-Dihydroxyvitamin D
  • Chronic kidney disease (↓ 1α-hydroxylation)
  • Severe vitamin D deficiency (low substrate)
  • Hypoparathyroidism
  • Chronic liver disease
  • Inherited defects in vitamin D metabolism
  • Long-term anticonvulsant therapy

References

  1. Kratz A, Ferraro M, Sluss PM, Lewandrowski KB. Laboratory reference values. N Engl J Med. 2004;351:1548–1563. PMID: 15470219
  2. Abbassi-Ghanavati M, Greer LG, Cunningham FG. Pregnancy and laboratory studies: a reference table for clinicians. Obstet Gynecol. 2009;114:1326–31. PMID: 19935037