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

Why Is This Test Done?

Your healthcare provider may order this test to check if you have enough vitamin D in your blood. This can be important if you have symptoms like muscle weakness, bone pain, or if you’ve had limited sun exposure, certain dietary restrictions, or conditions that affect vitamin D absorption (e.g., kidney disease, malabsorption). It may also be used to monitor vitamin D levels after treatment for deficiency.

What to Expect Before the Test

No special preparation is usually needed. You may be asked to fast for 8–12 hours before the test if it involves drawing blood from a vein. If you’re taking vitamin D supplements, let your provider know so they can adjust instructions.

What to Expect During the Test

A healthcare professional will draw blood from a vein in your arm. You may feel a small pinch, but it usually doesn’t cause discomfort. The blood is then sent to a lab for analysis.

What the Results Mean

Results help determine if your vitamin D levels are sufficient, low, or high. Low levels may require supplements or lifestyle changes (like more sun exposure or dietary adjustments), while high levels may need monitoring to avoid excess.