In most states, individuals can have their vitamin D levels tested by presenting a doctor's order at a laboratory facility, according to Quest Diagnostics. No preparation is necessary prior to testing vitamin D levels, which involves giving a small blood sample.
A vitamin D blood test, called 25-hydroxy vitamin D, is the most accurate measurement of how much vitamin D is in the body, according to MedlinePlus. Normal levels range from 30 to 74 nanograms per milliliter. Several factors contribute to low vitamin D levels, including lack of exposure to the sun, insufficient vitamin D in the diet, liver disease, kidney disease, problems absorbing vitamin D and using certain medications, such as phenobarbital and rifampin. Low vitamin D levels occur more often in African American children and infants who are only breastfed.
Vitamin D plays several important roles in the body, such as maintaining strong and healthy bones, helping fight infections, and keeping the brain, muscles, heart and lungs working properly, according to the Vitamin D Council. A lack of vitamin D is associated with many health conditions, including depression, cancer, asthma, type 2 diabetes and Alzheimer's disease. Autoimmune diseases, such as Crohn's disease, multiple sclerosis and type 1 diabetes, are also associated with vitamin D deficiency.