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The vitamin D test, also known as hydroxyvitamin D or 25 (OH) D test, aims to check the concentration of vitamin D in the blood, as it is an essential vitamin for the regulation of blood phosphorus and calcium levels, having a fundamental role in bone metabolism, for example.
This test is usually requested by the doctor to monitor replacement therapy with vitamin D or when there are signs and symptoms related to bone decalcification, such as muscle pain and weakness, for example, most of the time being requested together with the dosage of calcium, PTH and phosphorus in the blood.
What is it for
The vitamin D test is done mainly to diagnose vitamin D deficiency, in addition to hypervitaminosis D. However, the doctor may also order this test when there are signs and symptoms of bone decalcification, since vitamin D is one of the factors responsible for regulating the concentration of calcium and phosphorus, in addition to promoting bone mineralization.
This test is also required to monitor replacement therapy with vitamin D and to assist in the differential diagnosis of rickets, osteoporosis and osteomalacia, which is a disease characterized by fragile and brittle bones in adults. For this, in addition to the dosage of vitamin D, it may be requested to evaluate the levels of calcium, parathormone and phosphorus in the blood, since phosphorus is also related to the bone formation process. Understand how the blood phosphorus test is done.
In addition to being indicated to investigate hypo and hypervitaminosis and bone disorders, the vitamin D test is indicated for people who are considered at risk, who are those over 60, who have contraindications to sun exposure or who are not regularly exposed to sun, pregnant women and breastfeeding women, people with endocrine disorders, people with kidney disease or malabsorption syndromes or people who use drugs that can interfere with the formation and degradation of this vitamin.
This indication exists because this group of people has a higher risk of developing complications related to changes in the levels of this vitamin, and it is important that they are regularly monitored and undergo treatment according to the medical recommendation, which is often done through vitamin supplementation. D. Know more about vitamin D.
How the exam is done
To perform the exam, it is not necessary to perform any preparation, being done by drawing a small amount of blood, which is sent to the laboratory for analysis.
Vitamin D is produced from a substance derived from cholesterol present in the skin, which when stimulated by the ultraviolet light of the sun, is converted into cholecalciferol, known as vitamin D. The vitamin D produced undergoes metabolism in the liver, becoming 25- hydroxyvitamin D, which in the kidneys, under the influence of parathormone, is converted to 1,25-dihydroxyvitamin D, which corresponds to the active and stable form of vitamin D and is responsible for increasing the absorption of calcium in the intestine and, consequently, increasing the concentration of calcium in the blood.
Both forms of vitamin D are dosed, with 25-hydroxyvitamin D being most often used to identify vitamin D deficiency, while 1,25-dihydroxyvitamin D is usually required for people with kidney disease.
What the results mean
From the results of the dosage of 25-hydroxyvitamin D, it is possible to indicate whether the person has sufficient amounts of vitamin D circulating in the blood to maintain bone health. According to the 2017 recommendation of the Brazilian Society of Clinical Pathology / Laboratory Medicine and the Brazilian Society of Endocrinology and Metabology [1], sufficient levels of vitamin D are:
- For healthy people:> 20 ng / mL;
- For people belonging to the risk group: between 30 and 60 ng / mL.
In addition, it is determined that there is a risk of toxicity and hypercalcemia when vitamin D levels are above 100 ng / mL. Regarding the levels considered insufficient or deficient, studies are being carried out with this objective, however it is recommended that people who present values below the recommended are accompanied by the doctor and, according to the identified level, the most appropriate treatment is started.
Decreased vitamin D levels
The decreased values of vitamin D indicate hypovitaminosis, which may be due to little exposure to the sun or little intake of foods rich in vitamin D or its precursors, such as egg, fish, cheese and mushrooms, for example. Discover other foods rich in vitamin D.
In addition, diseases such as fatty liver, cirrhosis, pancreatic insufficiency, inflammatory disease, rickets and osteomalacia and diseases that lead to inflammation in the intestine can lead to vitamin D deficiency or deficiency. Know how to recognize the symptoms of vitamin D deficiency.
Increased values of vitamin D
The increased values of vitamin D are indicative of hypervitaminosis, which happens due to the use of large amounts of vitamin D for a long period. Prolonged exposure to the sun does not result in hypervitaminosis, as the body is able to regulate the amount of vitamin D and when optimal concentrations are identified, it is indicated that the synthesis of vitamin D by the stimulation of the sun is interrupted and, therefore, there are no toxic levels. of vitamin D due to prolonged exposure to the sun.