The serum concentration of calcifediol, also called 25-hydroxyvitamin D (abbreviated 25(OH)D), is typically used to determine vitamin D status. Most vitamin D is converted to 25(OH)D in the serum, giving an accurate picture of vitamin D status. The level of serum 1,25(OH)D is not usually used to determine vitamin D status because it often is regulated by other hormones in the body such as parathyroid hormone. The levels of 1,25(OH)D can remain normal even when a person may be vitamin D deficient. Serum level of 25(OH)D is the laboratory test ordered to indicate whether or not a person has<unk>  or insufficiency. It is also considered reasonable to treat at-risk persons with vitamin D supplementation without checking the level of 25(OH)D in the serum, as vitamin D toxicity has only been rarely reported to occur. Levels of 25(OH)D that are consistently above 200 nanograms per milliliter (ng/mL) (or 500 nanomoles per liter, nmol/L) are potentially toxic. Vitamin D toxicity usually results from taking supplements in excess. Hypercalcemia is often the cause of symptoms, and levels of 25(OH)D above 150 ng/mL (375 nmol/L) are usually found, although in some cases 25(OH)D levels may appear to be normal. Periodic measurement of serum calcium in individuals receiving large doses of vitamin D is recommended.
Vitamin D deficiency
Vitamin D toxicity
Endocrine bone disease
Metabolic bone disease
Disorders of calcium metabolism
Steroid-induced osteoporosis
Molybdenum deficiency
Mineral deficiency