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 many food products, such as milk and cereals. You can also get it as supplements, often combined with calcium.

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.

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.