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

Why Is This Test Done?

Your doctor may order this test if you have symptoms like muscle weakness, bone pain, or if you’re at higher risk for vitamin D deficiency, such as not getting enough sunlight or having limited sun exposure. It’s also used to monitor vitamin D levels in people with conditions like osteoporosis, kidney disease, or malabsorption disorders.

What to Expect Before the Test

No special preparation is needed, but you may be asked to fast for 8–12 hours before the test if it involves drawing blood from your vein. If you’re taking vitamin D supplements, your doctor may advise stopping them for a few days before testing.

What Happens During the Test?

A healthcare provider will draw blood from a vein in your arm. You may feel a slight pinch, but the procedure usually takes a few minutes. The blood sample is then sent to a lab for analysis.

What the Results Mean

Results are typically reported in nanograms per milliliter (ng/mL) or picomoles per liter (pmol/L). While reference ranges vary by lab, low levels may indicate deficiency, while very high levels could signal overuse of supplements or certain medical conditions.