Calcitriol, Total Unit Converter

Calcitriol, also known as 1,25-dihydroxyvitamin D, is the most biologically active form of vitamin D. It is the final product of the vitamin D activation pathway.

Vitamin D from sunlight or diet is first converted to 25-hydroxyvitamin D (calcidiol) in the liver, then to calcitriol in the kidneys. While calcidiol is the standard marker of overall vitamin D status, calcitriol is the hormonally active form that directly regulates calcium and phosphorus levels in the body.

Calcitriol has a short half-life of about 5 to 8 hours, compared to calcidiol which circulates for weeks. Its production is tightly regulated by parathyroid hormone (PTH), calcium, phosphorus, and FGF23.

Calcitriol is produced primarily in the proximal tubule cells of the kidneys, where the enzyme 1-alpha-hydroxylase converts calcidiol (25-hydroxyvitamin D) into its active form. Small amounts are also produced by activated macrophages and the placenta.