Serum or plasma concentration of vitamin D (25-hydroxyvitamin D)

Why Is This Test Done?

Your doctor may order this test if you have symptoms like bone pain, muscle weakness, or if you’re at higher risk for vitamin D deficiency, such as not getting enough sunlight, having limited sun exposure, or having certain medical conditions. It’s also used to monitor vitamin D levels after treatment for deficiency.

What to Expect Before the Test

No special preparation is needed. You may have a small needle inserted into a vein (usually in your arm) to draw blood. If you’re tested for plasma, your doctor may ask you to fast for a few hours before the test, but this depends on the lab’s instructions.

What the Results Mean

Results are typically reported as a numeric value representing the concentration of vitamin D in your blood. While reference ranges vary by lab, low levels may suggest deficiency, while higher levels may indicate over-supplementation or other conditions. Your doctor will interpret results in the context of your health and symptoms.

Common Causes of Low or High Levels

Low vitamin D levels can result from limited sun exposure, poor diet, certain medical conditions (like kidney or liver disease), or medications that interfere with vitamin D absorption. High levels may occur from over-supplementation or certain genetic conditions.