Vitamin D (25-Hydroxyvitamin D), Total

The Vitamin D (25-hydroxyvitamin D), Total test measures the level of vitamin D in the blood. This form of vitamin D reflects the total amount from both vitamin D2 and D3 sources. Vitamin D is essential for calcium absorption, bone health, immune function, and overall wellness.

1. What Is Vitamin D?

• Vitamin D is a fat-soluble vitamin that comes in two main forms: D2 (from plant sources and supplements) and D3 (from sunlight exposure and animal sources).

• The liver converts both forms into 25-hydroxyvitamin D (25(OH)D), which is the best indicator of overall vitamin D status.

• The kidneys then convert 25(OH)D into its active form (1,25-dihydroxyvitamin D).

2. Why Is the Vitamin D Test Performed?

This test is used to:

• Assess vitamin D levels to ensure adequate bone and immune health.

• Diagnose vitamin D deficiency or toxicity.

• Monitor treatment with vitamin D supplements.

• Evaluate patients with bone disorders, osteoporosis, or chronic kidney disease.

3. Vitamin D Reference Range

• Deficient: < 20 ng/mL

• Insufficient: 20 – 29 ng/mL

• Sufficient: 30 – 100 ng/mL

• Potentially toxic: > 100 ng/mL (toxicity rarely occurs unless over-supplemented)

4. Interpreting Vitamin D Results

🔹 Low Vitamin D:

• Associated with bone loss, osteoporosis, rickets in children, and muscle weakness.

• Linked to increased risk of infections, autoimmune conditions, and mood disorders.

🔹 High Vitamin D:

• Usually due to excessive supplementation.

• Can lead to hypercalcemia (high calcium), causing nausea, kidney problems, or confusion.

5. What Can Affect Vitamin D Levels?

• Sun exposure (UVB rays stimulate vitamin D3 production in the skin)

• Dietary intake (e.g., fatty fish, fortified foods, supplements)

• Age, skin color, geographic location, and sunscreen use

• Medical conditions such as malabsorption, kidney disease, or liver disease

6. How Is the Test Performed?

• A blood sample is taken from a vein.

• Fasting is not typically required unless ordered with other tests.

7. When to See a Doctor

🚨 Speak with your healthcare provider if you:

• Experience fatigue, bone pain, frequent infections, or mood changes.

• Are at risk for deficiency (e.g., older adults, people with limited sun exposure).

• Are taking high-dose vitamin D supplements and need monitoring.

🔹 Key Takeaways

✅ Vitamin D is crucial for bone strength, immunity, and overall health.

✅ The 25-hydroxyvitamin D test is the most accurate way to assess vitamin D status.

✅ Supplementation and lifestyle changes can help maintain optimal levels.