Vitamin D (25-OH)
A blood test for vitamin D status; low levels are very common.
25-hydroxy vitamin D is the form measured to assess vitamin D status. Most labs flag under 20 ng/mL as deficient and 20-30 ng/mL as insufficient. Deficiency is common in winter, indoor workers, and people with darker skin, and is usually corrected with oral supplements.
Medically reviewed by Dr. Ikechukwu Ogbu, MD
MD · Board-Certified, Internal Medicine · Last reviewed June 2026