About Vitamin D
Vitamin D is a fat-soluble vitamin that is made by the body after exposure to ultraviolet rays from the sun. Vitamin D can also be obtained by taking supplements and from eating certain foods.
What does Vitamin D do in the body?
Vitamin D helps maintain normal blood levels of calcium and phosphorous. It aids in the absorption of calcium, helping to form and maintain strong bones. Vitamin D also modulates neuromuscular, immune and other cellular functions.
Why do physicians test for Vitamin D?
A physician generally will order a test to determine the level of vitamin D in a patient's body.
Several factors are associated with an increased risk of developing Vitamin D deficiency.
At risk populations include:
- Individuals with low dietary vitamin D levels: Infants fed only mother's milk and children who do not drink fortified milk are at risk.
- Individuals with malabsorption syndromes: Patients with pancreatic enzyme deficiency, Crohn disease, cystic fibrosis, celiac disease, and surgical resection of stomach or intestines are at risk.
- Individuals with severe liver disease: Hepatic disease can reduce the conversion of vitamin D to 25-D and can lead to malabsorption of vitamin D.
- Individuals with kidney disease: Nephrotic syndrome can increase the urinary loss of vitamin D.
- Individuals taking certain drugs: Several medications, including phenytoin, phenobarbital, and rifampin accelerate the breakdown of vitamin D by the liver.
- Individuals who live at higher latitudes: Individuals who live in northern climates are at increased risk of deficiency, especially in winter months due to diminished exposure to UVB radiation.
- Individuals who spend little time outside: Individuals who are home-bound or simply choose to remain inside are at increased risk.
- Older adults: The skin becomes less efficient at producing vitamin D as one ages because of diminished levels of vitamin D precursors in the skin.
- Individuals with decreased sun exposure for cultural reasons: Women in some societies are required to cover themselves with heavy clothing, reducing exposure to the sun's rays.
- Races with high melanin levels: Increased skin pigmentation can reduce the efficiency of vitamin D conversion in the skin as much as 50-fold. Individuals with dark complexions living at higher latitudes are at increased risk.
About the test
What does Vitamin D testing assess?
Vitamin D tests generally assess the total volume of 25-Hydroxyvitamin D (25OHD), which is the form of Vitamin D circulating in the blood. Vitamin D tests may also provide information on the levels of Vitamin D2 and D3, which comprise total Vitamin D levels
Use: Rule out vitamin D deficiency
Limitations: Values of vitamin D vary with exposure to sunlight. The assay measures other vitamin D metabolites, including dihydroxylated metabolites such as 24,25, 25,26, and 1,25 dihydroxy vitamin D; however, since the physiological concentrations of these metabolites are insignificant compared to those of 25-hydroxy vitamin D, the accuracy in assessing vitamin D levels is not compromised.
Cost: $159
Result time: 1-2 business days