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

Why Is This Test Done?

Your healthcare provider may order this test if you have symptoms like muscle weakness, bone pain, or if you’re at higher risk for vitamin D deficiency (e.g., limited sun exposure, certain medical conditions, or dietary habits). It’s also used to monitor vitamin D levels after treatment or supplementation.

What to Expect Before the Test

No special preparation is needed. You may have a blood draw, and the sample will be sent to a lab to measure vitamin D levels. If you’re taking vitamin D supplements, let your provider know, as this may affect results.

What the Results Mean

Results are typically reported as a concentration of vitamin D in the blood. While reference ranges vary by lab, low levels may indicate deficiency, while higher levels may suggest excess intake or other conditions. Your provider will interpret results in the context of your overall health.

Common Causes of Abnormal Results

Low levels may be due to insufficient sun exposure, poor diet, certain medications, or liver/kidney issues. High levels could result from over-supplementation or rare genetic conditions. Other factors, like obesity or certain medical conditions, may also influence results.