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Calcitriol in the blood
Last reviewed: 23.04.2024
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The reference concentration (norm) of calcitriol in the blood serum in adults is 16-65 pg / ml (42-169 pmol / l).
Vitamin D 3 (cholecalciferol) is formed in the skin of 7-dehydrocholesterol under the influence of sunlight or enters the body with food. The synthesized and received vitamin D 3 is transported by blood to the liver, where in the mitochondria it is converted to 25-hydroxyvitamin [25 (OH) D 3 ]. This intermediate is converted to either 1.25 (OH) 2 D 3, or 24.25 (OH) 2 D 3. Calcitriol [1,25 (OH) 2 D 3 ] is formed in the mitochondria of kidney cells under the action of 1-hydroxylase, this is the most active form of vitamin D 3. 1,25 (OH) 2 D 3 is actually a hormone, it has a direct antirachitic effect, the mechanism of its action is similar to that of steroid hormones. After synthesis in the kidneys, it is transported by blood to the intestine, where in the cells of the mucosa stimulates the synthesis of calcium-binding protein, which is able to bind calcium coming from food (this is the main function of vitamin D). As a result of these processes, the concentration of calcium in the blood rises. The formation and secretion of 1,25 (OH) 2 D 3 in the kidneys is affected by the content of calcium and phosphorus in food. An excess of 1,25 (OH) 2 D 3 inhibits the synthesis of PTH. An increase in the concentration of calcium in the blood, caused by an excess of 1,25 (OH) 2 D 3, also inhibits the release of PTH. Prolactin and STH are important regulators of vitamin D metabolism during pregnancy and growth.
The disadvantage of 1,25 (OH) 2 D 3 leads to hypocalcemia, osteomalacia and related disorders. Low concentrations of 1,25 (OH) 2 D 3 in the blood are detected in rickets, osteoporosis after the onset of menopause, osteomalacia, hypoparathyroidism, in adolescents with type 1 diabetes mellitus, metastases in the bone, chronic renal insufficiency.
Elevated concentrations of 1,25 (OH) 2 D 3 in the blood are detected in primary hyperparathyroidism, sarcoidosis, tuberculosis, calcification, in normally growing children, pregnant and lactating women.
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