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

Why It’s Done

Your healthcare provider may order this test if you have symptoms of vitamin D deficiency, such as fatigue, muscle weakness, or bone pain. It’s also used to monitor vitamin D levels in people with conditions like osteoporosis, kidney disease, or those on certain medications that affect vitamin D metabolism. Some doctors check vitamin D levels regularly in people at higher risk of deficiency, such as those with limited sun exposure or certain dietary habits.

What to Expect

A blood sample is taken from a vein in your arm. You may feel a slight pinch, but it usually doesn’t cause discomfort. The blood is then sent to a lab for testing. Results are typically available within a few days.

How It Works

The test measures 25-hydroxyvitamin D, a form of vitamin D found in your blood. This form is more stable and easier to measure than other forms of vitamin D in the body.

What the Results Mean

Low levels may indicate a deficiency, which can affect bone health and other body functions. High levels might suggest over-exposure to vitamin D or certain medical conditions. Your healthcare provider will interpret your results in the context of your overall health and medical history.