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. This can be important if you have symptoms like muscle weakness, bone pain, or if you’re at risk for conditions like osteoporosis or rickets. It may also be done if you’re taking certain medications that affect vitamin D levels or if you have a condition that impacts how your body uses vitamin D.

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 a blood draw, but this depends on the lab’s instructions. If you’re taking vitamin D supplements, let your provider know so they can adjust your results accordingly.

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 will be sent to a lab for testing.

What the Results Mean

Results are typically reported as a specific concentration unit (e.g., ng/mL or nmol/L). Low levels may indicate vitamin D deficiency, which can affect bone health and other body functions. High levels might suggest overabsorption or certain medical conditions. Your provider will interpret the results in the context of your overall health.