25-Hydroxyvitamin D Blood Test in Hawaii

What this test measures

Vitamin D supports calcium absorption and helps maintain healthy bones and muscles. The body makes it when skin is exposed to sunlight and takes in additional amounts from certain foods and supplements. The liver converts vitamin D into 25-hydroxyvitamin D, also called calcidiol, which is the main form measured in blood. Because calcidiol reflects overall vitamin D stores, it is the preferred marker for assessing vitamin D status.

The test requires a single blood sample, usually drawn from a vein in the arm. The laboratory reports the calcidiol concentration, and clinicians compare it with reference ranges that vary by laboratory and by the group being tested. Vitamin D can also be assessed through related markers, but the 25-hydroxy form remains the standard for routine evaluation of deficiency or excess.

People may be tested when they have risk factors for low vitamin D, such as limited sun exposure, darker skin, older age, or conditions that affect fat absorption. It may also be ordered to monitor replacement therapy or to investigate bone pain, muscle weakness, or frequent fractures. A provider interprets the result with the person's history rather than in isolation.