Clinical Significance

Vitamin D is a fat-soluble steroid prohormone mainly produced photochemically in the skin from 7-dehydrocholesterol.

Two forms of vitamin D are biologically relevant – Vitamin D3 (Cholecalciferol) and Vitamin D2 (Ergocalciferol). Both Vitamins D3 and D2 can be absorbed from food, with Vitamin D2 being an artificial source, but only an estimated 10-20% of vitamin D is supplied through nutritional intake. Vitamins D2 and D3 can be found in vitamin supplements. Vitamin D is converted to the active hormone 1,25-(OH)2-vitamin D(calcitriol) through two hydroxylation reactions. The first reaction occurs in the liver, converting Vitamin D into 25-OH vitamin D. The second reaction, occurring in the kidneys, converts 25-OH vitamin D into the biologically active 1,25(OH)2-vitamin D. The major storage form of vitamin D is 25-OH vitamin D(half-life of 2-3 weeks) and is present in the blood at up to 1,000 fold higher concentration compared to the active 1,25(OH)2-vitamin (half-life of 4 hours).This assay measures 25-OH Vitamin D.

Measurement of Vitamin D status provides opportunities for preventive and therapeutic interventions for Vitamin D insufficiencies and deficiencies.

Vitamin D deficiency is a cause of secondary hyperparathyroidism, rickets, osteoporosis, osteomalacia. Reduced 25-OH vitamin D concentrations in blood have been associated with an increasing risk of chronic diseases, including common cancers, autoimmune or infectious diseases or cardiovascular problems.