Vitamin D Deficiency Testing Levels

Many people in the United States are vitamin D deficient. While experts recommend getting between 5 mcg and 15 mcg of vitamin D each day (depending on a person’s age), many people are unknowingly not getting enough of this nutrient.

Because low vitamin D levels are linked to a variety of health problems, from rickets to heart disease, it’s important to make sure you’re getting adequate amounts of vitamin D. Fortunately, testing vitamin D levels is relatively simple.

How Doctors Evaluate Vitamin D Levels

The most common way to evaluate vitamin D levels is with a blood test, called the 25-hydroxy vitamin D test. Doctors use this blood test to determine the amount of calcidiol (the form of vitamin D metabolized by your liver). Normal levels of vitamin D range from 30 to 74 nanograms per milliliter (ng/mL). According to the National Institutes of Health, a concentration of less than 15 nanograms of calcidiol per milliliter of blood indicates an inadequate level of vitamin D, and a concentration of less than 11 ng/mL indicates a vitamin D deficiency. However, some experts believe that anything less than 25 ng/mL may actually indicate a vitamin D deficiency. On the other end of the scale, concentrations of calcidiol that exceed 200 nanograms per milliliter of blood are considered to be potentially toxic.

A doctor may order a vitamin D test if he suspects you are deficient in vitamin D. Signs of vitamin D deficiency include muscle pain, bone pain and weakness. If you are in a group that is at high risk for vitamin D deficiency (for example, people who have little exposure to the sun or have dark skin), your health care provider may also consider a vitamin D test. If you are about to begin taking drugs to treat osteoporosis, are elderly and have little sun exposure, or are exhibiting symptoms of rickets or osteomalacia, your doctor may also test your vitamin D levels.

Blood Testing for Vitamin D Levels

A blood test is the most accurate way to determine if you have low vitamin D levels. To perform the test, your doctor or other healthcare provider will use a needle to draw blood from one of your veins (often from the back of your hand or the inside of your elbow). You should refrain from eating for the four hours prior to the test.

There are few risks associated with vitamin D testing, though some people may faint or feel light-headed, develop a hematoma (accumulated blood underneath the skin), excessive bleeding or infection. Talk to your healthcare provider beforehand if you are concerned about any of these risks. Sometimes, a doctor will also use X-rays to determine if you are vitamin D deficient.

Different tests, along with the different labs that evaluate blood samples, may result in variations in recorded concentrations of calcidiol [also known as 25(OH)D] in the blood. However, efforts are currently underway that aim to standardize the values obtained by different vitamin D tests.

Resources

National Institutes of Health, Office of Dietary Supplements. (2009). Dietary Supplement Fact Sheet: Vitamin D. Retrieved December 10, 2009, from the National Institutes of Health website: http://ods.od.nih.gov/factsheets/vitamind.asp.

Lab Tests Online. (n.d.). Vitamin D. Retrieved December 13, 2009, from the Lab Tests Online website: http://www.labtestsonline.org/understanding/analytes/vitamin_d/test.html.

MedlinePlus. (2008). 25-hydroxy vitamin D test. Retrieved December 13, 2009, from the National Library of Medicine webiste: http://www.nlm.nih.gov/medlineplus/ency/article/003569.htm.

Mayo Medical Laboratories. (n.d.). Vitamin D testing. Retrieved December 13, 2009, from the Mayo Medical Laboratories website: http://www.mayomedicallaboratories.com/articles/vitamind/index.html.

Merck Home Manual. (n.d.). Vitamin D. Retrieved December 13, 2009, from the Merck website: http://www.merck.com/mmhe/sec12/ch154/ch154j.html.