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 fatigue, muscle weakness, bone pain, or if you’re at higher risk for vitamin D deficiency. It’s also used to monitor vitamin D levels in people taking supplements or those with conditions like osteoporosis or kidney disease.

What to Expect Before the Test

No special preparation is needed for this blood test. You may be asked to fast for 8–12 hours before the draw if your lab requires it, but always follow your provider’s instructions. Wear a comfortable shirt and bring your ID for easy access to your blood.

What Happens During the Test?

A healthcare professional will insert a small needle into a vein in your arm to draw blood. The process usually takes a few minutes. You may feel a slight pinch, but it’s quick and rarely causes discomfort. The blood sample will be sent to a lab for analysis.

What the Results Mean

Results are compared to standard ranges for vitamin D, but exact values can vary by lab. Low levels may indicate deficiency, while high levels could signal overuse of supplements or certain medical conditions. Your provider will discuss the results with you and explain any actions needed.