What Is the 25-Hydroxy Vitamin D Test?
Vitamin D helps your body absorb calcium and maintain strong
bones throughout your entire life. Your body produces vitamin D when the sun’s
UV rays contact your skin. Other good sources of the vitamin include fish,
eggs, and fortified dairy products. It’s also available as a dietary
Vitamin D must go through several processes in your body before
your body can use it. The first transformation occurs in the liver. Here, your
body converts vitamin D to a chemical known as 25-hydroxyvitamin D, also called
The 25-hydroxy vitamin D test is the best way to monitor vitamin
D levels. The amount of 25-hydroxyvitamin D in your blood is a good indication
of how much vitamin D your body has. The test can determine if your vitamin D
levels are too high or too low.
The test is also known as the 25-OH vitamin D test and the
calcidiol 25-hydroxycholecalcifoerol test. It can be an important indicator
of osteoporosis (bone
weakness) and rickets (bone
Why Is a 25-Hydroxy Vitamin D Test Done?
Your doctor may request a 25-hydroxy vitamin D test for several
different reasons. It can help them figure out whether too much or too little
vitamin D is causing bone weakness or other abnormalities. It can also monitor
people who are at risk for having a vitamin D deficiency.
Those who are at high risk of having low levels of vitamin D
- people who don’t get much exposure to the sun
- older adults
- people with obesity
- babies who are breastfed only (formula is
usually fortified with vitamin D)
- people who have had gastric bypass surgery
- people who have a disease that affects the
intestines, such as Crohn’s disease. (This condition makes it difficult for
your body to absorb nutrients.)
Your doctor may also want you to do a 25-hydroxy vitamin D test
if they’ve already diagnosed you with a vitamin D deficiency and they want to
check if treatment is working.
How Is the 25-Hydroxy Vitamin D Test Performed?
Your doctor will tell you not to eat anything for four to eight
hours before the test.
The 25-hydroxy vitamin D test requires a common blood test. Your
doctor or a lab technician will draw blood from a vein in your arm using a
needle. A quick finger prick will more than likely provide enough for a blood
sample in children and infants.
Evaluating the Results of a 25-Hydroxy Vitamin D Test
No specific number range indicates vitamin D deficiency. Results
depend on your age, gender, and the testing methods used. Results can also slightly
vary from lab to lab.
Low blood levels of
25-hydroxy vitamin D usually mean one (or more) of the following:
- you aren’t eating a balanced, complete diet
- your intestines aren’t absorbing the vitamin
- you’re not spending enough time outside to
absorb adequate vitamin D levels through sun exposure
Some evidence links vitamin D deficiency to a higher risk of
certain cancers, immune diseases, and cardiovascular disease.
High vitamin D blood
levels generally result from taking too many vitamin pills and
other nutritional supplements. High doses of vitamin D can result in a
condition called hypervitaminosis
D. Hypervitaminosis is a rare but serious condition that could put you
at risk for liver or kidney problems.
High levels are rarely due to consuming too much of the vitamin
through foods or sun exposure.
Your doctor will help explain the results of your test and
determine if you have a vitamin D deficiency.
Risks of a 25-Hydroxy Vitamin D Test
As with any routine blood test, risks of the 25-hydroxy vitamin
test are minimal and include:
- excessive bleeding
- a slight chance of infection where the needle
pierces your skin
Vitamin D is vital to the body. Deficiencies at any age can cause
problems. Your doctor may recommend supplements or other treatment options if
you’re very deficient. Eating foods that contain vitamin D in addition to
adding supplements to your regimen can help keep your vitamin D levels stable.