Description
1,25-dihydroxycholecalciferol, also known as calcitriol, is the most biologically active form of vitamin D, acting as a hormone to regulate calcium and phosphate levels, crucial for bone health, immune function, and cell growth, primarily produced in the kidneys from 25-hydroxyvitamin D (calcidiol) and essential for calcium absorption, though the standard vitamin D screening test measures calcidiol, while calcitriol tests are used for specific bone or kidney disorders.
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Calcium Regulation:
It significantly increases intestinal absorption of calcium and phosphate and reduces their excretion by the kidneys, keeping levels stable in the blood.
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Bone Health:
By controlling calcium and phosphorus, it helps in bone mineralization and prevents conditions like rickets and osteoporosis.
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Hormonal Action:
It binds to vitamin D receptors (VDR) in cells, influencing gene expression, and also suppresses the production of parathyroid hormone (PTH).
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Immune System:
It plays a role in modulating immune responses, suppressing inflammation, and inhibiting certain immune cells (Th1).
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Formation:
Vitamin D from sunlight or diet (cholecalciferol) is converted in the liver to 25-hydroxyvitamin D (calcidiol), which is then converted in the kidneys by the enzyme 1α-hydroxylase to the active calcitriol.
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Standard Test:
The routine blood test for vitamin D deficiency checks 25-hydroxyvitamin D levels, reflecting total body stores.
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Specialized Test:
The 1,25-dihydroxyvitamin D test (calcitriol) is used to investigate specific issues with kidney function, parathyroid glands, or complex bone diseases, rather than general deficiency.
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Medication:
Calcitriol is used therapeutically to treat low calcium (hypocalcemia) and bone diseases.
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Diagnosis:
Abnormal levels can point to kidney disease, disorders of the parathyroid glands, or specific vitamin D metabolism problems.
