Vitamin D3 (25-Hydroxy Vitamin D)
Also known as: 25-OH Vitamin D, Calcidiol Test, Cholecalciferol Test, Vitamin D Total
Parameters Measured in the Report
A breakdown of individual biomarkers and biological reference intervals typically found in your report:
| Biomarker | Standard Range | Unit | What It Means |
|---|---|---|---|
25-Hydroxy Vitamin D (Total 25-OH D) | Deficient: < 20 Insufficient: 20–29 Sufficient: 30–100 Toxicity: > 100 | ng/mL (or nmol/L = ng/mL × 2.5) | Primary circulating form reflecting total body stores from sunlight, diet, and supplements. |
* Note: Reference ranges may vary slightly between testing instruments and reagent kits. Always refer to the reference interval printed on your specific pathology report.
Clinical Focus
Total circulating concentration of 25-hydroxyvitamin D (D2 and D3 combined).
Sample & Specimen
Venous blood (Serum tube)
Fasting Protocol
No fasting required. Blood can be drawn at any convenient time.
Turnaround Time
12–24 hours
What Is This Test?
Why Did Your Doctor Order This Test?
Physicians routinely prescribe the Vitamin D in the following clinical scenarios:
How to Prepare Before Your Test
- No fasting is needed.
- If you are currently taking high-dose weekly vitamin D supplements (e.g., 60,000 IU), consult your doctor on whether to test right before your next dose.
Understanding Your Results
What higher or lower readings generally mean in clinical practice:
If Values Are Higher Than Normal
Levels above 100 ng/mL indicate hypervitaminosis D (potential toxicity), virtually always caused by excessive, unmonitored megadosing of oral supplements rather than sun exposure. Severe toxicity leads to hypercalcemia, kidney stones, nausea, and vascular calcification.
If Values Are Lower Than Normal
Deficiency (<20 ng/mL) leads to secondary hyperparathyroidism, accelerated bone demineralization (osteomalacia in adults, rickets in children), muscle weakness, and increased risk of osteoporosis and falls.
Frequently Asked Questions
Why can’t I get enough Vitamin D from food alone?
Very few natural foods contain substantial vitamin D (primarily fatty fish like salmon, egg yolks, and fortified milk). Sunlight synthesis on skin is the body’s primary natural pathway, which is often limited by indoor lifestyles and geography.
Related Laboratory Tests
Tests frequently prescribed together or used as follow-up investigations:
Serum Calcium & Phosphorus
Total circulating Calcium (free ionized plus albumin-bound) and Inorganic Phosphorus (Phosphate).
Intact Parathyroid Hormone (iPTH)
Biologically intact 84-amino acid polypeptide hormone secreted by the four parathyroid glands.
Vitamin B12 (Cyanocobalamin)
Total concentration of water-soluble vitamin B12 (cobalamin) in blood serum.
Medical & Diagnostic Disclaimer
This guide is published for educational and patient informational purposes only. It is not a substitute for professional medical evaluation, diagnosis, or clinical advice.
A laboratory result that falls slightly outside standard statistical reference intervals does not automatically indicate disease; conversely, a normal result does not guarantee the absence of medical conditions. Only your attending physician can interpret lab findings in the context of your medical history, physical exam, and symptoms.