What Is the Test for Vitamin D?

Vitamin D is a fat-soluble vitamin that helps you absorb calcium and build strong bones. The vitamin D test determines your vitamin D levels from a sample of blood drawn from your vein.

The test for measuring vitamin D involves measuring the levels of the vitamin in a blood sample drawn from your vein. You do not need to fast or prepare specially for the test. The collection of blood for the test usually takes less than five minutes. You can expect to get the test results within a day or two.

Vitamin D is a fat-soluble vitamin that plays a vital role in calcium absorption to give you healthy and strong bones. It exists in two forms:

Vitamin D2: You get your vitamin D2 from vitamin D-fortified foods such as cereals, milk and yogurt.

Vitamin D3: Your body makes vitamin D3 when it gets exposed to sunlight. It is also found in foods such as eggs and fish, such as salmon, sardines, tuna and mackerel.

Both the forms, vitamin D2 and vitamin D3, get converted to another form of vitamin D called 25 hydroxyvitamin D or 25(OH)D in your body. Doctors usually order the blood test that gives the blood levels of 25(OH)D. Another test measures the level of 1,25-hydroxyvitamin D, but this is used only in rare situations.

Experts have a different opinion about the levels of vitamin D that work for a particular person. Even laboratories do not use the same reference values for normal vitamin D levels. Do not assume things. Ensure that you take your results with you during your next visit to your doctor and discuss the results with them.

A vitamin D test checks for vitamin D deficiency in the body.

Your doctor may suspect you have low vitamin D levels if you suffer from:

• Bone pain
• Frequent joint pain
• Bone weakness
• Muscle pain or cramps
• Bone fracture
• Abnormal bone anatomy or structure such as bow legs or knock knees in children
• Fatigue
• Depression

Your doctor may do routine vitamin D testing if you are affected with conditions that include:

• Osteoporosis (brittle bones)
• Obesity
• Kidney disease
• Liver disease
• Cystic fibrosis
• Celiac disease
• Crohn’s disease
• Previous gastric bypass surgery

Your doctor may also order the test if you:

• Are older 
• Live in areas where there is a lack of sunlight
• Have been homebound for months

Make sure you always tell your doctor about all the medications you have been taking. Some medications can cause your vitamin D levels to become low. These include:

• Steroids
• Laxatives
• Medications for seizures
• Cholesterol-lowering drugs
• Orlistat (a drug for weight loss)
• Rifampin (medication for tuberculosis)

The best way to raise vitamin D levels naturally is to get exposed to the sunlight for 15 to 20 minutes at least three times a week. You can also consume vitamin D-rich foods such as milk and other dairy products (fortified with vitamin D), eggs, mushrooms and fatty fish (sardines, salmon, tuna and mackerel).

Depending upon how low your vitamin D levels are, what condition has caused it and how severe your signs and symptoms are, your doctor will usually recommend vitamin D supplements or pills. Make sure you take the supplements as recommended and do not self-treat yourself. Higher doses can lead to a condition known as vitamin D toxicity, a rare but life-threatening condition in which the vitamin D test will show increased vitamin D levels.