Description for Vitamin D Test
Formal name: 25-hydroxy-vitamin D (Calcidiol, Calcifidiol) and 1,25 dihydroxy-vitamin D (Calcitriol) is the most commonly ordered Vitamin D Test
Vitamin D is found in blood in two forms: 25 hydroxy Vitamin D and 1,25 dihydroxy Vitamin D. 25 hydroxy Vitamin D (25 OH Vitamin D) is the major form of the hormone found in the blood and is the inactive precursor to the active hormone 1,25 dihyroxy Vitamin D. Because of its long half-life and higher concentration, 25 OH Vitamin D is commonly measured to assess and monitor Vitamin D status in individuals.
Vitamin D is produced in the skin (vitamin D3, also called cholecalciferol) on exposure to sunlight and also is ingested in foods and supplements (vitamin D2, also called ergocalciferol).
The main role of Vitamin D is to help regulate the absorption of calcium, phosphorus, magnesium. The Vitamin D test is essential in monitoring the health and growth of bone.
The Vitamin D tests is precribed to check bone weakness, bone malformation, or abnormal metabolism of calcium.
Since vitamin D is a fat-soluble, the vitamin D test is sometimes used to monitor individuals with diseases that interfere with fat absorption, such as cystic fibrosis and Crohn's disease.
When evaluating the Vitamin D test, the concentration is measured by means of analysis of a blood sample drawn from the vein in the arm.
Purpose of the Vitamin D Test
To meassure the level of Vitamin D in blood in order to check for a problem related to bone metabolism or parathyroid function, possible Vitamin D deficiency or malabsorption, and to monitor some patients taking Vitamin D.
The Vitamin D test in blood is normally ordered to identify a possible deficiency in vitamin D, when calcium is low or the patient has symptoms of vitamin D deficiency, such as bone malformation in children (rickets) and bone weakness, softness, or fracture in adults (osteomalacia).
1,25 di OH Vitamin D test in blood is usually is ordered when calcium is high or the patient has a disease that might produce excess amounts of Vitamin D, such as sarcoidosis or some forms of lymphoma.
The vitamin D test can also be used to diagnose problems with parathyroid gland functioning since parathyroid hormone is essential for vitamin D activation.
Reference range values for Vitamin D Test
ng/mL (SI: nmol/L = 2.496 x ng/mL)
optimum levels: 25-80 ng/ mL
toxicity: >80 ng/mL
Abnormal findings for Vitamin D Test
Low Vitamin D test levels of 25 hydroxy Vitamin D can mean that you are not getting enough exposure to sunlight or enough dietary vitamin D to meet your body’s demand or that there is a problem with its absorption from the intestines.
Occasionally, drugs such as phenytoin, can interfere with the production of 25 OH Vitamin D in the liver.
High levels of 25 hydroxy Vitamin D found in the vitamin D test normally means excess supplementation from vitamin pills.
Low levels of 1,25 di OH Vitamin D found in the vitamin D test can be seen in kidney disease.
High levels of 1,25 di OH Vitamin D found in the vitamin D test can be seen when there is excess parathryoid hormone or when there are diseases, such as sarcoidosis or some lymphomas, that can excess 1,25 di OH Vitamin D outside of the kidneys.