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

Why This Test Is Done

Your healthcare provider may order this test if you have symptoms of vitamin D deficiency, such as muscle weakness, bone pain, or frequent infections. It may also be recommended for people at higher risk, like those with limited sun exposure, certain medical conditions, or those who follow restrictive diets.

What to Expect Before the Test

No special preparation is needed. You may have a blood sample drawn from a vein in your arm, or urine/other fluid may be collected depending on the lab’s protocol. Tell your provider about any medications or supplements you take, as they can sometimes affect results.

What the Results Mean

Results are compared to standard ranges for vitamin D concentration in your blood. Low levels may indicate deficiency, while higher levels could be due to over-supplementation or other factors. Your provider will interpret results in the context of your overall health.

Common Causes of Abnormal Results

Low vitamin D levels can result from limited sun exposure, poor diet, certain medical conditions (e.g., kidney or liver disease), or medications that interfere with absorption. High levels may be caused by excessive vitamin D supplements or rare conditions.