Vitamin D Testing
Vitamin D testing is useful for finding out if you are vitamin D deficient before you start supplementing.
It is also helpful for re-checking your vitamin D level after a few months of supplementation, to make sure you are nicely in the optimum range.
You can order this test at your doctors office, or from a pathology lab. This type of blood test involves having a small amount of blood taken from a vein in your arm by a nurse or doctor, using a syringe. (Did you know, this procedure is called a phlebotomy?)
In some countries outside the US you are not permitted to order your test directly from a pathology lab.
Most people agree that extracting your blood for a test doesn’t hurt, except for a momentary prick when the needle is inserted.
If you go to your doctor, you can discuss the results with him or her, and plan a dosage and testing strategy together. This is definitely the route to follow if you are already under a doctor’s care for any specific condition.
You can also order a home test for vitamin D. This involves ordering your test online from a pathology lab and waiting for the kit to arrive by post. Using the pricker supplied, you prick your finger to collect a drop of blood, and post this off to the lab for testing. This is probably the easiest route for most people, unless you especially enjoy hypodermics. You can order a home vitamin D test from ZRT Laboratory.
The correct vitamin D test is called a 25(OH)D blood test. It measures the amount of storage-form vitamin D (total calcidiol) in your blood.
There is another kind of vitamin D blood test, usually called 1,25(OH)2D. (Note the name is very similar.) This one measures the amount of activated vitamin D (calcitriol) in your blood, but is not suitable for finding out if you are getting enough vitamin D.
If your doctor orders the test for you, make sure he or she knows which one you want.
Vitamin D Blood Test Results
Your pathology lab will report the result in either ng/ml or nmol/L. This example is in ng/ml:
Vitamin-D 25(OH)D 16.7 ng/ml (ref: 25 to 100 ng/ml)
In this example, 16.7 ng/ml is the actual blood test result. (This person was vitamin D deficient – most people are!) The reference range indicates the range or spread of vitamin D values normally found in healthy people. Different labs show different ranges. The lab may go into more detail and give a table similar to the one below.
|Vitamin D Status||25(OH)D Blood Level|
|High but not Toxic||66-100||164-250|
|Toxicity Possible||Above 100||Above 250|
As you see, we recommend an optimum range between 50 to 65 ng/ml (or 125 to 163 nmol/L). This is the level which is sustained naturally by healthy individuals who spend a proportion of each day in the sun, without much clothing – just as our ancestors have been doing for the last two million years, or so.
This is the vitamin D level we want to reach, and ideally, maintain all year round.
When you take the vitamin D blood test you will know if you are deficient, or not, and can plan your dosage strategy accordingly.
A vitamin D blood test is the only way to find out exactly what your vitamin D blood level is, but it may not be the only way of establishing that you are vitamin D deficient. See Vitamin D Estimating.