POWER OF VITAMIN D

                                                                                                                              

Vitamin D Test


 Itis easy to diagnose vitamin D deficiency: It’s a simple blood test. That’s all! However, it needs to be the right test and must be interpreted properly! And that’s where a lot of problems arise. 

What’s the Right Test to Diagnose Vitamin D Deficiency and Why?

 Laboratories offer two tests to determine vitamin D level in the blood. In vitamin D deficiency, one of them is low whereas the other one is often normal.  Most physicians don’t know the distinction between these two tests and may order the wrong test. Consequently, they may say your vitamin D level is normal, when it’s actually low.

 The right blood test to evaluate your vitamin D status is:

25 (OH) vitamin D (25-hydroxy vitamin D ).

  The other blood test for vitamin D is 1,25 (OH)2 vitamin D (1,25 dihydroxy vitamin D).

This is the wrong test to diagnose vitamin D deficiency!  Why?

There are two reasons why 25 (OH) vitamin D and not 1,25 (OH)2 vitamin D is the right test to diagnose vitamin D deficiency.

Reason 1:

25 (OH) vitamin D stays in your blood for a much longer period of time (half life of about 3 weeks) compared to 1,25 (OH)2 vitamin D (half life of about 14 hours).

Therefore, 25 (OH) vitamin D more accurately reflects the status of vitamin D in your body. 

Reason 2:

As vitamin D deficiency develops, your body increases production of parathyroid hormone by the parathyroid glands situated in your neck. Parathyroid hormone increases the conversion of 25 (OH) vitamin D into 1,25 (OH)2 vitamin D. Consequently, 1,25 (OH)2 vitamin D level in the blood will stay in the normal range (and can even be high) even if you’re low in 25 (OH) vitamin D.

  

CASE STUDY

       Jenny, was a 63 years old Caucasian female who got her vitamin D testing done.

The tests included 1,25 (OH)2 vitamin D as well as 25 (OH) vitamin D.

Her 1,25 (OH)2 vitamin D turned out to be high as 72 pg/ml (reference range 15-55 pg/ml). Her 25 (OH) vitamin D level was extremely low as 5 ng/ml (30- 100 ng/ml).

Her parathyroid hormone level was markedly elevated as 571 pg/ml (reference 12-65 pg/ml).

          Her diagnosis was secondary hyperparathyroidism due to severe vitamin D deficiency. If she only had the 1,25 (OH)2 vitamin D level done, her diagnosis of severe vitamin D deficiency would have been missed because her 1,25 (OH)2  vitamin D was not low, but high.

           Her 1,25 (OH)2 vitamin D level was high due to her high level of  parathyroid hormone which converted 25 (OH) vitamin D into 1,25 (OH)2 vitamin D. In fact, she was very low in vitamin D as was accurately demonstrated by her very low level of 25 (OH) vitamin D.

 

 

  

Interpretation of the Lab Test

 

To complicate matters further, the normal range reported by most laboratories for vitamin D is outdated and incorrect. Most physicians unfortunately simply interpret a blood test in reference to the “normal range” provided by the lab.

 

Consequently, physicians may incorrectly advise their patients that their vitamin D level is fine, even when it’s not.

 

Why are the normal ranges for 25 (OH) vitamin D inaccurate?

 

The normal ranges for vitamin D come from the era when our concern was just to prevent rickets. A small dose of vitamin D is enough to prevent rickets. Therefore, a level of 25 (OH) vitamin D of 10 ng/ml (25 nmol/L) or above was established as adequate to prevent rickets. That’s why many laboratories report 10 ng/ml (25 nmol/L) as the lower limit of the normal range.

 However, in recent years our understanding of the effects of vitamin D has dramatically changed. Now we understand that vitamin D can do much more than simply prevent rickets. In fact, vitamin D is crucial for maintaining many vital functions in the body, such as a healthy immune system and a healthy heart. In addition, an adequate level of vitamin D helps prevent diabetes, osteoporosis and cancer, as discussed earlier.

To achieve these goals, many experts in the field (including myself) recommend a level of 25 (OH) vitamin D to be at least 30 ng/ml (75 nmol/L) and preferably above 50 ng/ml (125 nmol/L). An excellent review of scientific studies (1) published in the American Journal of Clinical Nutrition in 2006 concluded that the most beneficial blood level of 25 (OH) vitamin D starts at 30 ng/ml (or 75 nmol/L). 

 Unfortunately many laboratories continue to report a normal range with the lower limit of 10 ng/ml (25 nmol/L). Now imagine the following scenario: Your 25 (OH) vitamin D level is19 ng/ml.;  Your physician interprets this as normal because it’s in the “normal range” provided by the laboratory. However, you are actually quite low in vitamin D! This happens all too frequently.

 

Watch out for the units used by the Laboratory.

 

There is another problem that many physicians are unaware of. Different laboratories report vitamin D level in different units. In the U.S. and around the world, most laboratories report 25 (OH) vitamin D in one of two ways: either as ng/ml or nmol/L. 

The conversion factor from ng/ml to nmol/L is about 2.5. For example, if your level is 30 ng/ml, you multiply it by 2.5 and will get a number of 75 in nmol/L. The lower limit of normal for 25 (OH) vitamin D should be 30 ng/ml or 75 nmol/L. 

Now, let’s assume that you are fortunate enough to have a physician who keeps up with the latest information and is proactive about vitamin D supplementation. From attending conferences and reading articles on vitamin D, your physician may simply remember that the lower limit of normal for 25 (OH) vitamin D is 30 (and that’s how most physicians remember - just the numbers, without paying attention to the units).  

Here’s another treacherous case scenario: Your laboratory reports your 25 (OH) vitamin D to be 40 nmol/L. Your physician simply looks at the number 40 and tells you your vitamin D is good. In his mind, it’s more than 30, so you’re fine. In fact, your vitamin D is low because in reality, a level of 40 nmol/L is equal to 16  ng/ml.!!  He totally forgot to look closely at the units. 

Also, note that the upper limit of normal as reported by many laboratories is also inaccurate. The upper limit of normal should be 100 ng/ml (250 nmol/L).

 

Excerpts from"Power of Vitamin D" by Dr. Sarfraz Zaidi, a ground breaking book on vitamin D.

We obtained written permission from Dr. Zaidi to include this vital information in this website.

Treatment of Vitamin D deficiency