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

Why This Test Might Be Ordered

Your doctor may recommend 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 in people taking supplements or those with conditions like osteoporosis.

What to Expect Before the Test

No special preparation is usually needed, but you may be asked to fast for 8–12 hours before the draw if your lab uses a specific method. Bring your lab results or questions to your appointment.

What the Results Mean

Low levels may indicate deficiency, which can affect bone health, muscle function, or immune response. High levels might suggest over-supplementation or certain medical conditions. Your doctor will interpret results in relation to your overall health.

Common Reasons for Testing

Common reasons include diagnosing deficiency, checking vitamin D levels after starting supplements, or evaluating symptoms like fatigue, bone pain, or frequent infections.