Calcitriol 1,25-Dihydroxyvitamin D
The calcitriol 1,25-dihydroxyvitamin D test measures the hormonally active vitamin D metabolite synthesised by renal 1α-hydroxylase. It is ordered to investigate dysregulated calcium and phosphate metabolism, not vitamin D deficiency. Elevated calcitriol characterises granulomatous disease and some lymphomas;
1
Biomarkers
Blood (serum)
Sample
3–5 business days
Turnaround
No
Fasting
What is the Calcitriol test?
The Calcitriol 1,25-Dihydroxyvitamin D test measures serum concentration of the hormonally active vitamin D metabolite. Unlike 25-hydroxyvitamin D — the marker of vitamin D status — calcitriol is ordered to investigate disordered calcium and phosphate metabolism, unexplained hypercalcaemia or hypocalcaemia, and suspected dysregulation of the vitamin D endocrine axis. It is a second- or third-line test, requested after intact PTH, 25-hydroxyvitamin D, calcium, phosphate, and renal function have framed the clinical picture. Calcitriol concentration reflects the balance of renal synthesis and peripheral catabolism rather than vitamin D intake or stores, so practitioners order it when they suspect inappropriate production — extrarenal synthesis in granulomatous disease or lymphoma, inadequate renal synthesis in chronic kidney disease or hereditary rickets, or paradoxical elevation in the setting of hypercalcaemia. Serial calcitriol is also used to monitor replacement therapy in hypoparathyroidism and certain forms of rickets.
What does the Calcitriol test measure?
Calcitriol is the hormonally active form of vitamin D, synthesised in the proximal renal tubule by 1α-hydroxylase acting on 25-hydroxyvitamin D. It binds the nuclear vitamin D receptor to regulate calcium and phosphate homeostasis, intestinal absorption, bone mineralisation, and parathyroid hormone secretion. Despite its central role, circulating calcitriol concentration is tightly controlled by parathyroid hormone, fibroblast growth factor 23, calcium, and phosphate, and its half-life is short — around four to six hours — making it a poor index of vitamin D stores but an essential window into dysregulated vitamin D metabolism.
Calcitriol measurement is reserved for investigating disorders of vitamin D metabolism and calcium homeostasis, not for assessing vitamin D sufficiency. Elevated calcitriol is seen in granulomatous diseases (sarcoidosis, tuberculosis), some lymphomas, and primary hyperparathyroidism, while low calcitriol characterises chronic kidney disease, hypoparathyroidism, vitamin-D-dependent rickets, and hereditary phosphate-wasting disorders. Unlike 25-hydroxyvitamin D, calcitriol remains normal or even elevated in simple vitamin D deficiency because secondary hyperparathyroidism drives renal 1α-hydroxylase.
Why is the Calcitriol test ordered?
- Investigation of unexplained or PTH-independent hypercalcaemia, particularly when sarcoidosis, tuberculosis, or lymphoma is in the differential
- Work-up of hypocalcaemia with low or inappropriately normal calcitriol, suggesting hypoparathyroidism or renal 1α-hydroxylase deficiency
- Evaluation of chronic kidney disease patients with refractory secondary hyperparathyroidism or hypocalcaemia, to assess endogenous calcitriol production
- Diagnosis of hereditary vitamin-D-dependent rickets types I and II, guided by clinical and biochemical features
- Assessment of hypophosphataemic rickets or tumour-induced osteomalacia, where calcitriol is inappropriately low for the degree of hypophosphataemia
- Monitoring replacement with calcitriol or alfacalcidol in hypoparathyroidism, to titrate dose and avoid hypercalcaemia
- Follow-up of granulomatous disease being treated for vitamin-D-mediated hypercalcaemia
Sample collection and turnaround
Sample type
Blood (serum)
Fasting required
No
Collection method
Venipuncture at patient service centre
Turnaround
3–5 business days
Collection notes
Phlebotomy via Quest; no fasting is required. Samples should be drawn into a serum separator tube, protected from light, and centrifuged promptly. Calcitriol is labile, so delayed processing can lower measured concentration.
Specimen requirements
Minimum 1 mL serum. Protect from light; separate serum within two hours of collection and freeze if not assayed immediately. Note the performing laboratory for serial comparability, as assays differ.
What can affect Calcitriol results?
Exogenous active vitamin D metabolites raise serum calcitriol concentration; timing relative to the last dose affects interpretation.
PTH stimulates and FGF23 suppresses renal 1α-hydroxylase, so primary hyperparathyroidism can elevate calcitriol and chronic kidney disease or FGF23 excess reduces it.
Low serum calcium and phosphate both stimulate 1α-hydroxylase, raising calcitriol as a homeostatic response unless renal synthesis is impaired.
Progressive nephron loss reduces 1α-hydroxylase capacity, so calcitriol concentration falls as GFR declines, typically below 30 mL/min/1.73 m².
Unlike 25-hydroxyvitamin D, calcitriol shows minimal seasonal variation because its synthesis is hormonally regulated rather than substrate-limited in healthy individuals.
Calcitriol assays are technically demanding, and results can differ between laboratories; samples should be protected from light and separated promptly to prevent degradation.
What do Calcitriol results mean?
Elevated
Extrarenal production of calcitriol in granulomatous disease (sarcoidosis, tuberculosis, berylliosis), granuloma-forming lymphoma, or certain solid tumours; primary hyperparathyroidism (in which PTH-driven synthesis exceeds physiological need); and Williams syndrome. Inappropriately elevated calcitriol in the setting of hypercalcaemia is the hallmark of dysregulated extrarenal 1α-hydroxylase.
Normal
A calcitriol concentration within the reference range does not exclude vitamin D deficiency — most vitamin-D-deficient patients have normal or even elevated calcitriol because secondary hyperparathyroidism drives renal synthesis. Interpretation requires the full mineral panel and PTH.
Reduced
Impaired renal synthesis in chronic kidney disease (stage 3–5), hypoparathyroidism (loss of PTH stimulus), vitamin-D-dependent rickets type I (hereditary 1α-hydroxylase deficiency), FGF23 excess in X-linked hypophosphataemia or tumour-induced osteomalacia, and pseudohypoparathyroidism (PTH resistance). Low calcitriol with hypocalcaemia suggests inadequate activation; low calcitriol with hypophosphataemia points to FGF23-mediated suppression.
Note: Calcitriol is not a screening test and does not correlate with 25-hydroxyvitamin D stores. Its short half-life and tight hormonal regulation mean that a single result is a snapshot; the pattern with PTH, calcium, phosphate, FGF23, and renal function determines the diagnosis. Reference intervals vary by laboratory, and results on active vitamin D therapy are not interpretable without timing relative to the last dose.
Frequently asked questions
25-Hydroxyvitamin D (calcidiol) is the storage form and the best marker of vitamin D sufficiency. Calcitriol is the active hormone, produced by the kidneys, and is ordered to investigate disorders of vitamin D metabolism — not to assess vitamin D status.
How to access the Calcitriol test
The Calcitriol reference page is free and open to all practitioners. Create a free practitioner account to see pricing, save tests to your list, and generate requisition forms. Verification takes 1–2 business days.
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Published: October 7, 2026
Last reviewed: October 7, 2026
- Bilezikian JP, et al. Hypoparathyroidism in the adult: epidemiology, diagnosis, pathophysiology, target-organ involvement, treatment, and challenges for future research. J Bone Miner Res. (2011)
- Sharma OP. Vitamin D, calcium, and sarcoidosis. Chest. (1996)
- KDIGO clinical practice guideline for the diagnosis, evaluation, prevention, and treatment of chronic kidney disease–mineral and bone disorder. (2017)
- Carpenter TO, et al. A clinician's guide to X-linked hypophosphatemia. J Bone Miner Res. (2011)
- Bikle DD, Patzek S, Wang Y. Physiologic and pathophysiologic roles of extra renal CYP27b1: case report and review. Bone Rep. (2018)
This content is for licensed healthcare practitioners only and does not constitute medical advice. Clinical decisions should be based on the full clinical picture and not on any single test result.
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