Calcitriol (1,25 di-OH Vitamin D)
The calcitriol test measures serum 1,25-dihydroxyvitamin D, the hormonally active form of vitamin D synthesised by renal 1α-hydroxylase. It is not a measure of vitamin D status — 25(OH)D is used for that — but a diagnostic tool for hypercalcaemia from granulomatous disease or lymphoma, CKD–mineral bone disorder, hereditary rickets, and hypoparathyroidism, interpreted with calcium, phosphate,…
1
Biomarkers
Blood (serum)
Sample
3–5 business days
Turnaround
No
Fasting
What is the Calcitriol test?
The Calcitriol (1,25 di-OH Vitamin D) test measures the serum concentration of the hormonally active form of vitamin D. Practitioners order it not to assess vitamin D sufficiency — 25-hydroxyvitamin D is the appropriate test for that — but to investigate specific disorders of calcium, phosphate, and vitamin D metabolism where calcitriol itself is thought to be abnormally produced or regulated. Calcitriol is useful in the work-up of hypercalcaemia when granulomatous disease or lymphoma is suspected, because activated macrophages and malignant cells can express extrarenal 1α-hydroxylase and generate calcitriol autonomously. It is also measured in chronic kidney disease to understand disordered mineral metabolism, in hereditary vitamin-D-dependent rickets, in hypoparathyroidism where low PTH may suppress renal calcitriol synthesis, and occasionally in refractory hypocalcaemia or unexplained bone disease. A normal or elevated calcitriol in the face of low 25-hydroxyvitamin D indicates compensatory upregulation and does not negate the need to replète vitamin D stores.
What does the Calcitriol test measure?
Calcitriol is the hormonally active form of vitamin D, synthesised in the renal tubules by 1α-hydroxylase from 25-hydroxyvitamin D. Its primary function is to maintain calcium and phosphate homoeostasis by increasing intestinal absorption of calcium, promoting renal calcium reabsorption, and mobilising calcium from bone in conjunction with parathyroid hormone. Calcitriol is tightly regulated by parathyroid hormone, fibroblast growth factor 23, calcium, and phosphate concentrations, and its circulating half-life is only a few hours. Serum calcitriol levels may be normal or even elevated despite vitamin D deficiency, because secondary hyperparathyroidism drives 1α-hydroxylase activity to sustain calcium absorption.
Calcitriol measurement is reserved for specific diagnostic questions — hypercalcaemia work-up (granulomatous disease, lymphoma), chronic kidney disease with suspected abnormal vitamin D metabolism, hereditary rickets, hypoparathyroidism, and suspected 1α-hydroxylase deficiency. It is not used to assess vitamin D status; 25-hydroxyvitamin D is the correct test for that purpose. An elevated calcitriol in the setting of hypercalcaemia points to extrarenal production, as occurs in sarcoidosis and some malignancies.
Why is the Calcitriol test ordered?
- Evaluation of hypercalcaemia when sarcoidosis, tuberculosis, or other granulomatous disease is suspected, or in lymphoma with unexplained elevated calcium
- Work-up of chronic kidney disease–mineral and bone disorder, particularly when 25(OH)D is replete but hypocalcaemia or hyperparathyroidism persists
- Investigation of hereditary vitamin-D-dependent rickets (types I and II), where mutations affect 1α-hydroxylase or the vitamin D receptor
- Assessment of hypoparathyroidism with unexplained low calcium, to determine whether insufficient calcitriol production contributes to hypocalcaemia
- Refractory hypocalcaemia or osteomalacia when 25-hydroxyvitamin D is normal and primary causes have been excluded
- Monitoring of patients on active vitamin D analogues (alfacalcidol, calcitriol) for chronic kidney disease or hypoparathyroidism, to avoid toxicity
- Rare cases of suspected tumour-induced osteomalacia or paraneoplastic hypercalcaemia with suspected ectopic calcitriol production
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 LabCorp draw site; no special preparation. Calcitriol is light-sensitive and has a short half-life, so specimen handling must be prompt. Some laboratories request that the sample be protected from light during transport.
Specimen requirements
Minimum 1.0 mL serum, separated promptly and frozen if not analysed within a few hours. Consult the performing laboratory for specific handling instructions, as calcitriol is less stable than 25-hydroxyvitamin D. Note the assay platform for serial comparability.
What can affect Calcitriol results?
PTH stimulates renal 1α-hydroxylase, so secondary hyperparathyroidism (due to low calcium or vitamin D deficiency) raises calcitriol even when 25(OH)D is low; this compensatory elevation is physiological and does not indicate vitamin D sufficiency.
Progressive nephron loss reduces 1α-hydroxylase capacity, lowering calcitriol production and contributing to renal bone disease and secondary hyperparathyroidism.
FGF23 suppresses 1α-hydroxylase and enhances 24-hydroxylase, lowering calcitriol synthesis; this is relevant in chronic kidney disease, tumour-induced osteomalacia, and hereditary hypophosphataemic rickets.
Activated macrophages in granulomata and some malignant lymphoid cells express extrarenal 1α-hydroxylase, producing calcitriol outside normal feedback control and causing hypercalcaemia.
Low phosphate stimulates 1α-hydroxylase, raising calcitriol as a homoeostatic response; hypophosphataemia should be interpreted alongside calcitriol.
Patients receiving calcitriol, alfacalcidol, or paricalcitol have pharmacological circulating levels; measurement is used to monitor therapy and avoid toxicity rather than to assess endogenous production.
What do Calcitriol results mean?
Elevated
Extrarenal 1α-hydroxylase activity (sarcoidosis, tuberculosis, lymphoma, histoplasmosis), primary hyperparathyroidism (though often normal), Williams syndrome, idiopathic infantile hypercalcaemia, or exogenous active vitamin D therapy. Elevated calcitriol with hypercalcaemia and suppressed PTH points strongly to granulomatous disease or lymphoma.
Normal
A normal calcitriol does not exclude vitamin D deficiency — 25(OH)D is the储存 form and the correct screening test. Normal calcitriol with low 25(OH)D reflects compensatory hyperparathyroidism maintaining active hormone levels at the expense of bone health. Interpret calcitriol in the full context of calcium, phosphate, PTH, 25(OH)D, and renal function.
Reduced
Chronic kidney disease (most common), vitamin-D-dependent rickets type I (1α-hydroxylase deficiency), hypoparathyroidism (low PTH drive), FGF23-mediated disorders (tumour-induced osteomalacia, X-linked hypophosphataemia), pseudohypoparathyroidism, or severe magnesium deficiency impairing PTH secretion. Low calcitriol with low calcium and elevated PTH is the hallmark of renal bone disease.
Note: Calcitriol is not a measure of vitamin D status; it is a tightly regulated hormone whose level may be sustained despite depleted stores. Its short half-life and diurnal variation make it less stable than 25(OH)D. Always measure 25(OH)D, calcium, phosphate, PTH, and creatinine alongside calcitriol to interpret the result correctly. Reference intervals vary by assay and laboratory.
Frequently asked questions
25-Hydroxyvitamin D is the storage form and the best marker of vitamin D status. Calcitriol is the active hormone, tightly regulated by PTH and kidney function, and may be normal or even elevated despite vitamin D deficiency. Practitioners use 25(OH)D to screen for deficiency and calcitriol only for specific diagnostic questions.
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
- Holick MF, et al. Evaluation, treatment, and prevention of vitamin D deficiency: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. (2011)
- KDIGO clinical practice guideline for the diagnosis, evaluation, prevention, and treatment of chronic kidney disease–mineral and bone disorder (CKD-MBD). Kidney Int Suppl. (2009)
- Sharma OP. Hypercalcemia in granulomatous disorders: a clinical review. Curr Opin Pulm Med. (2000)
- Bikle DD, Christakos S. New aspects of vitamin D metabolism and action — addressing the skin as source and target. Nat Rev Endocrinol. (2020)
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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