Vitamin D (25-OH)

Understanding the marker

The test measures 25-hydroxyvitamin D, the form used to assess vitamin D supply. Vitamin D helps regulate calcium and supports bone health.

The test measures 25-hydroxyvitamin D and can support assessment of suspected deficiency or selected bone and mineral conditions. Routine screening of otherwise healthy adults is not recommended. A low concentration alone does not establish the cause of fatigue or other nonspecific symptoms.

What does high Vitamin D (25-OH) mean?

A high vitamin D result is assessed with the level, calcium and any supplements or treatment. Excess vitamin D can affect calcium balance, so a marked elevation needs medical review rather than an automatic assumption about its cause.

What does low Vitamin D (25-OH) mean?

Low 25-hydroxyvitamin D can support a deficiency assessment. It does not on its own explain fatigue or nonspecific symptoms; any treatment depends on level, risk factors and clinical findings.