Vitamin D3 (1,25 Dihydroxycholecalciferol)
- Sample Type
- Serum
- Fasting
- No
- Unit
- pg/mL
Function
1,25-Dihydroxyvitamin D, also known as Calcitriol, is the biologically active form of Vitamin D. While the 25-hydroxy form is used to assess overall storage, this test measures the hormone produced by the kidneys through the action of 1-alpha-hydroxylase. Its primary function is to regulate calcium and phosphorus homeostasis by increasing intestinal absorption and modulating bone mineral density.
Why it is Ordered
This test is rarely used for screening general deficiency; instead, it is diagnostic for specific disorders. It is ordered when a patient has abnormal calcium levels, symptoms of hypercalcemia, or suspected sarcoidosis and other granulomatous diseases. It is also critical in monitoring patients with chronic kidney disease (CKD), as the failing kidney loses its ability to convert 25(OH)D into this active form.
Associated Conditions
- Hypocalcemia: Investigating the cause of low calcium when PTH is elevated.
- Chronic Kidney Disease: Monitoring secondary hyperparathyroidism.
- Granulomatous Diseases: Conditions like sarcoidosis or tuberculosis can lead to extra-renal production of 1,25-D, causing high calcium.
- Vitamin D-Dependent Rickets: Assessing genetic defects in the enzyme that converts Vitamin D.
Check Your Result
Check Your Result
Enter your lab result to see where you stand compared to the standard reference range.
Why Context Matters
Results can be significantly confounded by the patient's current calcium intake, parathyroid hormone (PTH) levels, and renal function. Biotin supplements can occasionally interfere with the immunoassay platforms used for this test. Furthermore, because 1,25-D has a very short half-life (hours) compared to 25-OH Vitamin D (weeks), it is highly sensitive to recent physiological fluctuations, making a second opinion or re-test valuable if results don't align with clinical symptoms.
Lab ranges are statistical averages, not biological laws. "Normal" for a 20-year-old male isn't normal for a 60-year-old female.
Clinical References
Source-of-truth databases and clinical guidelines for Vitamin D3 (1,25 Dihydroxycholecalciferol):
Official Sources
Research & Guidelines
Related Indicators
Medically Reviewed by Dr. Binoy Babu, MBBS
Board Certified Doctor • 10+ Years Clinical Experience
Dr. Babu is a practicing physician dedicated to empowering patients with clear, actionable medical information. He founded 2opi to bridge the gap between complex lab reports and patient understanding, ensuring everyone has access to a reliable second opinion.
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