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Calcitriol in the blood
Medical expert of the article
Last reviewed: 05.07.2025
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 from 7-dehydrocholesterol under the influence of sunlight or enters the body with food. Synthesized and ingested vitamin D 3 is transported by the blood to the liver, where it is converted into 25-hydroxyvitamin [25(OH)D 3 ] in the mitochondria. This intermediate product is converted either into 1,25(OH) 2 D 3 or into 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, 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 the blood to the intestine, where it stimulates the synthesis of calcium-binding protein in the cells of the mucous membrane, 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 increases. The formation and secretion of 1,25 (OH) 2 D 3 in the kidneys is affected by the calcium and phosphorus content in food. Excess 1,25 (OH) 2 D 3 inhibits the synthesis of PTH. An increase in the concentration of calcium in the blood caused by excess 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.
Deficiency of 1,25(OH)2D3 leads to hypocalcemia, osteomalacia and related disorders. Low blood 1,25(OH)2D3 concentrations are found in rickets ,postmenopausal osteoporosis, osteomalacia, hypoparathyroidism, in adolescents with type1 diabetes, bone metastases, and chronicrenal failure.
Elevated concentrations of 1,25(OH) 2D3in the blood are detected in primary hyperparathyroidism, sarcoidosis, tuberculosis, calcinosis, in normally growing children, pregnant and lactating women.
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