Vitamin D Total 25-Hydroxy (D2 & D3)
- Sample Type
- Serum
- Fasting
- No
- Unit
- ng/mL
Function
Vitamin D is a fat-soluble prohormone essential for calcium and phosphorus absorption in the gut. It exists in two primary forms: Vitamin D2 (ergocalciferol), derived from plants/fortified foods, and Vitamin D3 (cholecalciferol), synthesized in the skin via UV exposure. The 25-hydroxyvitamin D [25(OH)D] test measures the total concentration of both forms and is the gold standard for assessing a person's Vitamin D status because it has a long half-life in the blood.
Why it is Ordered
Vitamin D testing is requested to investigate bone pain, frequent fractures, or muscle weakness. It is a routine screening for individuals at risk of osteoporosis, those with malabsorption syndromes (like Celiac disease), or people with limited sun exposure. Recent research has also linked Vitamin D status to immune health, cardiovascular function, and mood regulation.
Associated Conditions
- Deficiency (<20 ng/mL): Leads to Rickets in children and Osteomalacia in adults. Chronic deficiency is a major risk factor for Osteoporosis.
- Insufficiency (21-29 ng/mL): Linked to increased parathyroid hormone (PTH) levels, which can lead to bone resorption.
- Toxicity (>150 ng/mL): Rare, but can cause hypercalcemia, leading to kidney stones, nausea, and cardiac arrhythmias.
Metabolic Pathway
After entering the bloodstream, Vitamin D is converted in the liver to 25(OH)D. It then travels to the kidneys, where it is converted into its active form, 1,25-dihydroxyvitamin D. Because 25(OH)D is the storage form, it provides the most accurate reflection of long-term levels.
Check Your Result
Check Your Result
Enter your lab result to see where you stand compared to the standard reference range.
Why Context Matters
Biotin supplements (often found in 'hair, skin, and nails' vitamins) can significantly interfere with the immunoassay used for Vitamin D, leading to falsely high or low results. Furthermore, Vitamin D levels fluctuate seasonally, often peaking in late summer and dropping in late winter. Recent high-dose supplementation can also cause a temporary spike that doesn't reflect long-term stores.
Lab ranges are statistical averages, not biological laws. "Normal" for a 20-year-old male isn't normal for a 60-year-old female.
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.
Get Notified When Dr. Babu Is Available