Calcitriol is the active form of Vitamin D. It is also known as 1,25(OH)2D. Calcitriol has long been known for its important role in regulating body levels of calcium and phosphorus, and in mineralization of bone.
Functions of Calcitriol:
Understanding Vitamin D Metabolism & Function:
The entry of vitamin D into the body is through the production of vitamin D in the skin upon exposure to sunlight (UVB) and through ingestion of either foods containing cholecalciferol (vitamin D3,) or ergocalciferol (vitamin D2) or dietary supplements of these substances.
The storage type of vitamin D, namely 25- hydroxy vitamin D (Calcidiol), is formed in the liver. This is the major circulating form of vitamin D, and the form that is currently used as a measure of one’s vitamin D status.
The hormone 1,25-dihydroxy vitamin D (Calcitriol) is formed in a second step in the kidney. The responsible enzyme, the kidney 1 α-hydroxylase, is subjected to a rigid control through hormones [especially PTH (parathyroid hormone)] and its activity is influenced by the serum concentrations of calcium and phosphate.
Importance of testing for Calcitriol levels:
Low calcitriol levels is one of the earliest changes to occur in persons with early kidney failure.
A high level of vitamin D 25-dihydroxy may occur when there is excess parathryoid hormone or when there are diseases, such as sarcoidosis or some lymphomas, that can make calcitriol outside of the kidneys.
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