Description

Vitamin D, 25-OH (25-hydroxyvitamin D) is the major circulating form of vitamin D in the blood and the best indicator of overall vitamin D status. This form reflects both dietary intake and vitamin D produced by the skin from sun exposure. It is eventually converted by the kidneys into the active form, 1,25-dihydroxyvitamin D (calcitriol).

Why the Vitamin D, 25-OH Test Is Important

A blood test for 25-hydroxyvitamin D is commonly used to:

  • Assess Vitamin D Deficiency or Insufficiency – Low levels are associated with fatigue, bone pain, muscle weakness, and increased risk of osteoporosis.
  • Monitor Supplementation – Helps determine if vitamin D supplementation is adequate or needs adjustment.
  • Evaluate Bone Health – Essential in assessing causes of bone thinning (osteopenia or osteoporosis) or unexplained fractures.
  • Support Chronic Disease Management – May be ordered for individuals with autoimmune disorders, certain cancers, or cardiovascular conditions where vitamin D status plays a role.

Low levels of 25-OH vitamin D are common and may result from limited sun exposure, poor diet, malabsorption, or certain medical conditions.

Fasting: Not required.