Vitamin D 1, 25-Dihydroxy

A vitamin D 1,25‑dihydroxy test measures the active form of vitamin D in blood to assess how the body converts and uses vitamin D. It's used when evaluating calcium balance, unexplained high or low calcium, kidney disease, parathyroid disorders, and conditions like sarcoidosis or lymphoma that alter vitamin D activation. It helps guide diagnosis and treatment when abnormal calcium or bone metabolism is suspected.

25-hydroxyvitamin D (25(OH)D) is the main circulating storage form made in the liver; it reflects vitamin D status and is measured to assess deficiency. 1,25-dihydroxyvitamin D (1,25(OH)2D or calcitriol) is the kidney-produced active hormone that regulates calcium and phosphate; it’s short-lived and tightly regulated, so its level doesn’t reliably indicate overall vitamin D stores.

Normal 1,25‑dihydroxyvitamin D (calcitriol) levels are generally about 20–60 pg/mL (48–144 pmol/L), though reference ranges vary by laboratory and assay. Because 1,25(OH)2D is tightly regulated and affected by kidney function, clinicians usually measure 25‑hydroxyvitamin D for status assessment; interpretation should consider clinical context and lab-specific reference intervals. If abnormal, follow‑up testing and specialist input may be needed.

Elevated 1,25‑dihydroxyvitamin D (calcitriol) most often reflects increased conversion of 25‑OH to 1,25‑OH2D from excess parathyroid hormone (eg, primary hyperparathyroidism) or ectopic 1‑alpha‑hydroxylase activity—often in activated macrophages—in granulomatous diseases (sarcoidosis, tuberculosis) and some lymphomas. Less commonly, certain medications, high‑dose vitamin D or rare activating mutations/tumors can raise calcitriol.

Low vitamin D is associated with low mood and a higher risk of depression; brain vitamin D receptors and effects on neurotransmitters and inflammation may contribute. Evidence is strongest for people who are deficient—supplementation can improve mood in those cases but is less clear for people with adequate levels. Test your vitamin D and discuss supplementation with your healthcare provider.

Vitamin D is measured as 25‑hydroxyvitamin D (25‑OH). General ranges: deficiency <20 ng/mL (<50 nmol/L); insufficiency 20–29 ng/mL (50–74 nmol/L); sufficient 30–50 ng/mL (75–125 nmol/L). Levels above ~150 ng/mL (>375 nmol/L) risk toxicity. Targets vary by guideline and individual factors, so discuss results and need for supplements with your clinician.