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Calcitriol (1,25-Dihydroxyvitamin D₃) in Serum/Plasma

Published: August 9, 2026Updated: August 15, 2026

This test measures the active form of vitamin D in your blood, which helps regulate calcium and bone health. Low levels may indicate vitamin D deficiency or malabsorption issues.

Quick summary

["Active vitamin D levels help maintain bone health and calcium balance; check if you have deficiency or metabolic disorders."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 15, 2026Editorial policy

Key facts at a glance

LOINC
33788-1
Short code
CALCPOST1
Synonyms
Calcit sp1 p chal SerPl-mCnc
Category
chemistry
Sample
serum
Container
Serum separator tube (SST) or red-top tube without anticoagulant for serum; alternatively, plasma separator tube (PST) with lithium heparin for plasma
Units
N/A
Ref low
0
Ref high
11.5
Fasting
false
Population
adult
Sex
all
Age range
≥ 0 years
Method
Chemiluminescent Immunoassay (CLIA) or Electrochemiluminescence Immunoassay (ECLIA)
CPT
82308
SNOMED
39579002
Specimen volume
1-2 mL of serum or plasma (minimum 0.5 mL)
Stability
Serum/plasma stable for 8 hours at room temperature (20-25°C), 24 hours refrigerated at 2-8°C, and up to 30 days frozen at -20°C or colder. Avoid repeated freeze-thaw cycles.
Hemolysis max
100
Lipemia max
300
Icterus max
25
TAT
24–72 hours
Order
routine

Why Is This Test Done?

Your healthcare provider may order this test if you have symptoms of vitamin D deficiency (e.g., bone pain, muscle weakness) or if you’re at higher risk (e.g., limited sun exposure, malabsorption disorders like celiac disease). It may also be used to monitor treatment for conditions like osteoporosis or rickets.

What to Expect Before the Test

No special preparation is needed. You’ll provide a blood sample, usually drawn from a vein in your arm. If you’re on vitamin D supplements, let your provider know—it may affect results.

What the Results Mean

Results help determine if your active vitamin D levels are within a healthy range. Low levels may signal vitamin D deficiency or kidney issues, while very high levels could indicate over-supplementation or certain liver disorders.

Common Conditions Linked to Results

Low active vitamin D levels are often linked to osteoporosis, rickets in children, or conditions like hypoparathyroidism. High levels may be associated with hypercalcemia or rare metabolic disorders.

Reference range

Reference values vary by stimulation protocol and laboratory methodology. Basal calcitonin levels: Male <11.5 pg/mL, Female <4.6 pg/mL. Post-stimulation (typically pentagastrin or calcium): peak calcitonin levels vary; consult laboratory-specific reference data. A stimulated calcitonin level >100 pg/mL in males or >50 pg/mL in females is suggestive of medullary thyroid carcinoma (MTC).N/A

Specimen: serum

No special patient preparation required. Patient should be in a supine position prior to specimen collection. For stimulation testing, the challenge substance (pentagastrin 0.5 mcg/kg IV or calcium gluconate 2 mg/kg IV over 1 minute) should be administered and the post-challenge specimen drawn at the designated time point as specified in the protocol (typically 2, 5, and 10 minutes post-injection).

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

This test is critical for diagnosing and managing vitamin D deficiency, which can lead to weakened bones, muscle weakness, or other health complications. It’s also used to assess kidney function, as the kidneys play a key role in activating vitamin D. Elevated levels may require further evaluation to rule out over-supplementation or secondary causes.

Short name

Vitamin D Active Metabolite

Frequently asked questions

What causes low active vitamin D levels?
Low levels can result from insufficient sun exposure, poor diet (low vitamin D intake), malabsorption disorders (e.g., celiac disease, Crohn’s), kidney disease, or liver problems. Age-related changes in vitamin D metabolism may also play a role.
What should I do if my results are low?
If your results are low, your provider may recommend increasing vitamin D-rich foods (e.g., fatty fish, fortified dairy), sunlight exposure, or supplements under medical supervision. Follow-up tests may be needed to monitor improvements.
Can vitamin D supplements affect this test?
Yes, high doses of vitamin D supplements can temporarily raise active vitamin D levels. Always discuss your supplement regimen with your provider before testing to avoid misleading results.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 15, 2026. · Read our editorial policy