Serum or plasma concentration of active vitamin D (1,25-dihydroxyvitamin D)

Why This Test Is Done

Your healthcare provider may order this test if you have symptoms of vitamin D deficiency, such as bone pain, muscle weakness, or unexplained fractures. It may also be used to monitor vitamin D levels in people with conditions like osteoporosis, kidney disease, or those taking vitamin D supplements. Sometimes, it’s part of routine screening for those at higher risk of deficiency.

What to Expect Before the Test

No special preparation is needed for this blood test. You may have a small needle inserted into your arm to draw blood, similar to other routine blood tests. If you’re on blood thinners or have a history of bleeding issues, let your provider know beforehand.

What the Results Mean

Results are typically reported as a concentration of the active vitamin D metabolite in the blood. While reference ranges can vary slightly by lab, lower levels may indicate insufficient vitamin D, while higher levels could suggest over-supplementation or certain medical conditions. Your provider will interpret results in the context of your overall health.

Common Conditions Monitored

This test is often used to diagnose or monitor conditions like rickets (in children), osteomalacia (softening of bones in adults), or vitamin D deficiency-related bone diseases. It may also help evaluate kidney function, since the kidneys play a key role in activating vitamin D.