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Vitamin D Test

Test Overview

A vitamin D test measures the amount of vitamin D in the blood. 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 also added to many food products, such as milk, orange juices, yogurts, margarines, and soy beverages. You can also get it as a natural health product, often combined with calcium.

Vitamin D recommendations vary from province to province. Talk with your doctor about how much vitamin D you need. Health Canada and Osteoporosis Canada recommend that Canadian adults take daily vitamin D supplements.

The vitamin D test is also called the 25-hydroxy vitamin D, or 25(OH)D, test.

Why It Is Done

In Alberta, you can only get this blood test if you have a medical condition that could be affected by low levels of vitamin D. This includes medical conditions such as:

  • Blood calcium levels that are too high or too low.
  • Bone diseases (such as osteoporosis or Paget’s disease).
  • Problems absorbing nutrients (such as celiac disease, small intestine surgery, taking medicines for seizures).
  • Chronic (long-term) kidney or liver disease.

Most healthy Albertans don’t need a vitamin D test. Vitamin D test results likely won’t change the advice from your healthcare provider. What’s important is that you try to get enough vitamin D from the sun, foods, and supplements.

To learn more about vitamin D supplements and other sources of vitamin D, talk to your healthcare provider or see:

How To Prepare

There is nothing to do to prepare for this test.

How It Is Done

Your health professional drawing blood will:

  • Wrap an elastic band around your upper arm to stop the flow of blood. This makes the veins below the band larger so it is easier to put a needle into the vein.
  • Clean the needle site with alcohol.
  • Put the needle into the vein. More than one needle stick may be needed.
  • Attach a tube to the needle to fill it with blood.
  • Remove the band from your arm when enough blood is collected.
  • Put a gauze pad or cotton ball over the needle site as the needle is removed.
  • Put pressure on the site and then put on a bandage.

How It Feels

The blood sample is taken from a vein in your arm. An elastic band is wrapped around your upper arm. It may feel tight. You may feel nothing at all from the needle, or you may feel a quick sting or pinch.

Risks

There is very little chance of a problem from having a blood sample taken from a vein.

  • You may get a small bruise at the site. You can lower the chance of bruising by keeping pressure on the site for several minutes.
  • In rare cases, the vein may become swollen after the blood sample is taken. This problem is called phlebitis. A warm compress can be used several times a day to treat this.

Results

A vitamin D test measures the amount of vitamin D in the blood.

The normal values listed here—called a reference range—are just a guide. These ranges vary from lab to lab, and your lab may have a different range for what's normal. Your lab report should contain the range your lab uses. Also, your doctor will evaluate your results based on your health and other factors. This means that a value that falls outside the normal values listed here may still be normal for you or your lab.

Vitamin Dfootnote 1

Normal:


50–150 nanomoles per litre (nmol/L) or 30–80 nanograms per millilitre (ng/mL)

High values

High levels of vitamin D can be caused by:

  • William's 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.

What Affects the Test

Medicines that may decrease vitamin D levels include:

  • Orlistat. Examples include Xenical. This is a weight-loss medicine.
  • Cholestyramine. Examples include Olestyr. This medicine lowers cholesterol levels.
  • Phenytoin. Examples include Dilantin. This medicine prevents seizures.

What To Think About

  • Vitamin D levels may change from spring and summer to fall and winter. Less sunlight in the fall and winter may cause lower vitamin D levels.
  • A test with a similar name is the 1,25-dihydroxyvitamin D test. This test does not give a good measurement of vitamin D levels.

References

Citations

  1. Pagana KD, Pagana TJ (2011). Vitamin D (25-hydroxy vitamin D). In Mosby's Manual of Diagnostic and Laboratory Tests, 4th ed., pp. 543–547. St. Louis: Mosby.

Credits

Adaptation Date: 5/5/2021

Adapted By: Alberta Health Services

Adaptation Reviewed By: Alberta Health Services

Adapted with permission from copyrighted materials from Healthwise, Incorporated (Healthwise). This information does not replace the advice of a doctor. Healthwise disclaims any warranty and is not responsible or liable for your use of this information. Your use of this information means that you agree to the Terms of Use. How this information was developed to help you make better health decisions.