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