vitamin d test

test overview

a vitamin d test measures the amount of vitamin d in the blood. the vitamin d test is also called the 25-hydroxy vitamin d, or 25(oh)d, test.

your body needs vitamin d to absorb calcium. calcium keeps your bones and muscles healthy and strong. if your muscles don't get enough calcium, they can cramp, hurt, or feel weak. you may have long-term (chronic) muscle aches and pains. if you don't get enough vitamin d throughout life, you are more likely to have thin and brittle bones (osteoporosis) in your later years.

children who don't get enough vitamin d may not grow as much as others their age. they also have a chance of getting a rare disease called rickets.

your body uses sunshine to make its own vitamin d. vitamin d is found in foods such as egg yolks, liver, and saltwater fish. it is added to some food products, such as milk and fortified soy or other plant-based beverages. you can also get it as supplements, often combined with calcium. osteoporosis canada recommends that canadian adults take daily vitamin d supplements. ^{footnote 1}

the vitamin d test is usually done in a doctor's office or a lab. or you may be able to buy an at-home version of the test. discuss the benefits and risks of at-home testing with your doctor before you buy one of these tests.

why it is done

you may need this test if you:

• have low levels of calcium or phosphate.
• have osteoporosis or low bone density.
• had a broken bone after a fall from standing, such as if you trip and fall. the break most commonly occurs in the hip or wrist.
• have gone through menopause and worry about osteoporosis.
• have low levels of vitamin d.

how to prepare

in general, there's nothing you have to do before this test, unless your doctor tells you to.

how it is done

a health professional uses a needle to take a blood sample, usually from the arm.

watch

how it feels

when a blood sample is taken, you may feel nothing at all from the needle. or you might feel a quick sting or pinch.

risks

there is very little chance of having a problem from this test. when a blood sample is taken, a small bruise may form at the site.

results

normal

each lab has a different range for what's normal. your lab report should show the range that your lab uses for each test. the normal range is just a guide. your doctor will also look at your results based on your age, health, and other factors. a value that isn't in the normal range may still be normal for you.

high values

high levels of vitamin d can be caused by:

• williams syndrome. this is a genetic problem that causes growth delays before and after birth.
• taking too many vitamin d supplements.

low values

low levels of vitamin d can be caused by:

• kidney disease.
• liver disease.
• not getting enough sunlight.
• not getting enough vitamin d in your diet.