We stand with Ukraine. 🇺🇦

Vitamin D, 25-Hydroxyvitamin D (Calcidiol)

SI UNITS (recommended)


* The SI units is the recommended method of reporting clinical laboratory results

Calcifediol, Calcidiol, 25-hydroxyvitamin D, 25-Hydroxycholecalciferol, 25-OH-D, 25(OH)D
Units of measurement
nmol/L, µg/L, µg/dL, µg/100mL, µg%, ng/mL

A steroid hormone that has long been known for its important role in regulating body levels of calcium and phosphorus and in the mineralization of bone. The term “vitamin D” specifically refers to two biologically inert precursors, vitamin D 3 (cholecalciferol) or D 2 (ergocalciferol). Neither vitamin D 3 nor vitamin D 2 has significant biologic activity; rather they must be metabolized within the body to the hormonally active form. Vitamin D3 is generated in the skin when light energy is absorbed (UV radiation in the UVB spectrum 290–320 nm) by a precursor molecule 7-dehydrocholesterol (7-DHC; provitamin D 3 ). However, cutaneous vitamin D3 production after single prolonged UVB exposure is capped at approximately 10–20% of the original epidermal 7-DHC concentration, a limit achieved with suberythemogenic UV exposures. Vitamin D2 is plant derived, produced exogenously by irradiation of ergosterol, and enters the circulation through diet. Vitamin D from the skin 3and vitamin D3 and D 2 from the diet enter the blood and are metabolized to their 25-hydroxy counterparts. Once formed, 25-hydroxyvitamin D (25-OHD) is metabolized in the kidney to 1,25-dihydroxyvitamin D (1,25-OHD).

  • Diagnosis of vitamin D deficiency
  • Differential diagnosis of causes of rickets and osteomalacia
  • Monitoring vitamin D replacement therapy
  • Diagnosis of hypervitaminosis D

Increased: Vitamin D intoxication, Excessive exposure to sunlight

Decreased: Malabsorption, Steatorrhea, Dietary osteomalacia, anticonvulsant osteomalacia, Biliary and portal cirrhosis, Thyrotoxicosis, Pancreatic insufficiency, Celiac disease, Inflammatory bowel disease, Rickets, Alzheimer disease

Lab units Conversion Calculator. Convert Vitamin D, 25-Hydroxyvitamin D (Calcidiol) level to nmol/L, µg/L, µg/dL, µg/100mL, µg%, ng/mL. Clinical laboratory units online conversion from conventional or traditional units to Si units. Table of conversion factors for Vitamin D, 25-Hydroxyvitamin D (Calcidiol).