Having blood tests to measure the amount of vitamin D in your blood is the only way to know if you’re getting enough vitamin D or not. The blood test you need is called a 25(OH)D blood test.
You can get a blood test at your doctors or you can do an in-home test or get a test at a laboratory. All of these methods of testing should give you accurate results.
In-home tests are easy to use and involve pricking your finger to take a small blood sample and sending this away to a laboratory for testing.
Your tests results will show whether you’re getting enough vitamin D or not, and whether you may need to take supplements or expose your skin to the sun more. Different organizations in the United States recommend different ideal vitamin D levels. The Vitamin D Council suggests that a level of 50 ng/ml is the ideal level to aim for.
How do I get tested?
There are three ways to get tested:
- Ask your doctor for a vitamin D test. Be specific and ask for a 25(OH)D test. There is another type of blood test for vitamin D, called a 1,25(OH)₂D test, but the 25(OH)D test is the only one that will tell you whether you’re getting enough vitamin D. If your health insurance covers a 25(OH)D test, this is a good way to work with your doctor to get tested.
- Order an in-home test. These tests are sent to your home. You prick your finger and put a drop of blood on to some blotter paper. You send the paper to a laboratory to be tested. These are an alternative if you don’t want to go to your doctor just for a vitamin D test, or if your insurance doesn’t cover a test.
- Order a test online and get blood work done at a laboratory. In the United States, there are a few websites that allow you to bypass your doctor and go straight to the testing laboratory. These websites include mymedlab.com, healthcheckusa.com and privatemdlabs.com. You can buy a 25(OH)D test from all of these companies and have the test itself done at your nearest LabCorp. These tests are a little more expensive than in-home tests.
All three ways of getting tested should give you an accurate result.
Where can I get an in-home test?
There are a number of companies that offer in-home tests, including:
- ZRT Labs. The Vitamin D Council works with ZRT Labs and receives 15% of the proceeds from each test bought. This helps to support the Vitamin D Council (a nonprofit organization!) and gives you accurate test results.
- New Century Diagnostics. The test is sold through a website called Home Health Testing. Some users report that the test is a little difficult to use.
- City Assays. This company is based in the UK and offers the cheapest test internationally (about $48 USD) and in the UK/Ireland (£25). It takes about 10 days for the test to arrive to the United States.
To the Vitamin D Council’s knowledge, all of these in-home tests are accurate.
Support the Vitamin D Council!
15% of the proceeds from the sale of each vitamin D ZRT test are donated to the Vitamin D Council. As the Council is a nonprofit organization, this is a great way to get involved in your health and support the organization at the same time.
How do I use a home testing kit?
Vitamin D Council has partnered with ZRT Labs to make available an in-home vitamin D testing kit. The test involves sending small samples of blood to a laboratory. ZRT’s Vitamin D Kit can be used to test vitamin D levels in both adults and children.
This is how the ZRT test works:
- Order a test; the test arrives at your door.
- The test kit provides everything you need. Prick your finger and place blood drops on the test card. The test requires two blood drops minimum but you can place up to twelve blood drops.
- Fill out form. Place form and completed test card into return envelope. You don’t need to fill out the form in full.
- Mail return envelope back to ZRT. If you live in the United States, the envelope is pre-paid and there are no costs in returning the envelope.
- ZRT will email your results back within a week. If you prefer snail mail, they can send results that way, too.
What do the results mean?
When you get your test results you will see a number in units of ng/ml, for example, 50 ng/ml. These are the units that health professionals in the United States use. Elsewhere in the world, vitamin D blood test results are given in units of nmol/l.
To convert a test result measured in nmol/l to one measured in ng/ml, divide the nmol/l number by 2.5. For example, 50 nmol/l is the same as 20 ng/ml (50÷2.5).
To convert a test result measured in ng/ml to one measured in nmol/l, multiply the ng/ml number by 2.5. For example, 20 ng/ml is the same as 50 nmol/l (20 x 2.5).
These are the ranges that different organizations in the United States use to say whether you’re severely lacking in vitamin D (deficient), mildly lacking in vitamin D (insufficient) or whether you’re getting enough vitamin D (sufficient):
|Vitamin D Council||Endocrine Society||Food and Nutrition Board||Testing Laboratories|
|Deficient||0-30 ng/ml||0-20 ng/ml||0-11 ng/ml||0-31 ng/ml|
|Insufficient||31-39 ng/ml||21-29 ng/ml||12-20 ng/ml|
|Sufficient||40-80 ng/ml||30-100 ng/ml||>20 ng/ml||32-100 ng/ml|
The Vitamin D Council suggests that a level of 50 ng/ml is the ideal level to aim for. This is why the Council recommends that adults take 5,000 IU/day of vitamin D supplement in order to reach and stay at this level.
The Endocrine Society recommends taking a vitamin D supplement of around 2,000 IU/day to reach and stay above a level of 30 ng/ml. This is what the Endocrine Society recommends as the ideal level to aim for. Lastly, the Food and Nutrition Board recommends 600 IU/day of vitamin D supplement because they believe 20 ng/ml is the ideal level to aim for.
What should you do based on your test results?
- If you tested low and want a higher level, you need to get more sun exposure or take a larger daily supplement.
- If you tested and are right where you want to be, continue your supplement and sun exposure routine. Keep in mind that your level in the summer is probably higher than in the winter, with more sun and UVB. So you may need to supplement more in the winter than in the summer to have the same vitamin D level.
- If you tested high and want a lower level, you need to take a smaller daily supplement.
You do not want to have a level over 100 ng/ml and in fact anything over 150 ng/ml is considered toxic. Go to the following pages for more information about your results, supplementation, and sun exposure:
- How do I get the vitamin D my body needs?
- I tested my vitamin D levels. What do my results mean?
- Am I deficient in vitamin D?
- Am I getting too much vitamin D?
- Holick MF, Binkley NC, Bischoff-Ferrari HA, Gordon CM, Hanley DA, Heaney RP, Murad MH, Weaver CM; Endocrine Society. Evaluation, treatment, and prevention of vitamin D deficiency: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. 2011 Jul;96(7):1911-30.
- Institute of Medicine, Food and Nutrition Board. Dietary Reference Intakes for Calcium and Vitamin D. Washington, DC: National Academy Press, 2010.
- Vieth, R. “The Pharmacology of Vitamin D.” In Vitamin D, Third Edition, by Feldman D, Pike JW and Adams JS. Elsevier Academic Press, 2011.