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. They might also recommend it if you have conditions like osteoporosis, kidney disease, or limited sun exposure. Pregnant women, older adults, or those with limited sun exposure are at higher risk and may need regular monitoring.

What to Expect Before the Test

No special preparation is needed, but you may be asked to fast for 8–12 hours before the blood draw if your lab uses a specific method. Wear comfortable clothing and plan to rest afterward, as drawing blood can make you feel lightheaded.

What Happens During the Test

A healthcare professional will insert a small needle into a vein in your arm to collect a blood sample. You may feel a brief pinch, but the process usually takes just a few minutes. The blood is then sent to a lab for analysis.

What the Results Mean

Results are typically reported as a numerical value indicating your vitamin D level, though exact ranges can vary by lab. Low levels may prompt further testing or dietary/sunlight adjustments, while normal levels confirm adequate vitamin D status.