Vitamin D Test

Why am I having this Vitamin D test?

Vitamin D is a vitamin that your body makes when you are exposed to sunlight. It is also found naturally in fish and eggs, and it is added to some foods, such as cereals and dairy products. You need vitamin D to maintain bone health and to support your disease-fighting (immune) system.

You may have a vitamin D test:

• To help diagnose osteoporosis or other bone disorders.
• To monitor treatment of osteoporosis or other bone disorders.
• If you have symptoms of a lack (deficiency) of vitamin D, such as experiencing broken bones from minor injuries.
• If you lack certain nutrients in your diet (dietary deficiencies).
• If you have problems absorbing nutrients during digestion.

What is being tested?

There are two types of vitamin D tests that measure slightly different things:

• The 25-hydroxyvitamin D test measures how much of a substance called 25-hydroxyvitamin D is in your blood. The body converts vitamin D to 25-hydroxyvitamin D in the liver. Measuring how much 25-hydroxyvitamin D is in your blood provides a good idea of your vitamin D levels. This is the most common type of vitamin D test.
• The 1,25-dihydroxyvitamin D test measures how much of a substance called 1,25-dihydroxyvitamin D is in your blood. The body converts vitamin D into this substance and then uses it for various functions. This test provides an idea of your total vitamin D levels.

What kind of sample is taken?

A blood sample is required for this test. It is usually collected by inserting a needle into a blood vessel or by sticking a finger with a small needle.

Tell a health care provider about:

• Any allergies you have.
• All medicines you are taking, including vitamins, herbs, eye drops, creams, and over-the-counter medicines.
• Any blood disorders you have.
• Any surgeries you have had.
• Any medical conditions you have.
• Whether you are pregnant or may be pregnant.

How are the results reported?

Your test results will be reported as a value that tells you how much vitamin D is in your blood. Your health care provider will compare your results to normal ranges that were established after testing a large group of people (reference ranges). Reference ranges may vary among labs and hospitals. For vitamin D tests, common reference ranges are:

• 25-hydroxyvitamin D: 25–80 ng/mL.
• 1,25-dihydroxyvitamin D:
  • Males: 18–64 pg/mL.
  • Females: 18–78 pg/mL.

What do the results mean?

If your result is within your reference range, this means that you have a normal amount of vitamin D in your blood.

If your result is lower than your reference range, this means that you have too little vitamin D in your body.

• If you had the 25-hydroxyvitamin D test specifically:
  • A result of 21–29 ng/mL means that you have slightly lower levels of vitamin D than normal (vitamin D insufficiency).
  • A result of 20 ng/mL or less means that you have very low levels of vitamin D (vitamin D deficiency).
• Low levels of vitamin D can result from:
  • Not having enough exposure to sunlight.
  • Not eating enough foods that contain vitamin D.
  • Osteoporosis.
  • Kidney disease.
  • Liver disease.
  • A bone disease that makes the bones weak, soft, or poorly developed (rickets).
  • Softening of the bones (osteomalacia).
  • The body not absorbing vitamin D normally (gastrointestinal malabsorption).

If your result is higher than your reference range, this means that you have too much vitamin D in your body. This can result from:

• Taking too many dietary supplements.
• Hyperparathyroidism. This is a rare condition in which you do not make enough of a certain type of hormone (parathyroid hormone or PTH).
• A disease that causes inflammation in your organs and other areas of your body (sarcoidosis).
• A rare developmental disorder that is present at birth (Williams syndrome).

Talk with your health care provider about what your results mean.

Questions to ask your health care provider

Ask your health care provider, or the department that is doing the test:

• When will my results be ready?
• How will I get my results?
• What are my treatment options?
• What other tests do I need?
• What are my next steps?

Summary

• You may have a vitamin D test to determine if your body has enough vitamin D. You need vitamin D to maintain bone health and to support your disease-fighting (immune) system.
• Your vitamin D level is determined with a blood test.
• Talk with your health care provider about what your results mean.