We (our Facebook Group) have recently confirmed through high-level management that both Quest and LabCorp measure P5P in our blood work. P5P is a form of B6 considered the active form.
Quest has a reference range of 2.1 – 21.7 ng/mL for those over 18. There is no gender difference. LabCorp has a reference range of 3.4 – 65.2. They used to have a gender difference but that was removed in summer of 2022. There is no age difference.
We also recently had some members who took Quest B6 labs hours apart from LabCorp B6 labs. We confirmed with these labs information that we already knew: LabCorp’s test will show lower B6 status than Quest’s results. In other words, a Quest test on the same day will read normal; whereas, a LabCorp test will read low normal.
On its website, LabCorp states the B6 test is to determine B6 deficiency. On it’s website Quest states the B6 test is to determine B6 deficiency and TOXICITY. The blood results actually reflect these words. LabCorp with its higher values of the blood work has set its methodology to find deficiency. Quest with its lower values has set testing methodology to include deficiency or toxicity.
What does this mean for our members? If you’re in the United States and you have a choice, then use Quest. If you don’t have a choice, then know that your lab values will be lower at LabCorp.
As you can see within the lab corporate world there is a good difference in what determines deficiency. Our question then becomes in the research world who has determined the parameters for deficiency? Do all the studies that are assuming B6 deficiency have to reevaluated?
I have been digging into research about B6 and the immune system. Most of the research suggests that the immune system is “bolstered” in a B6 deficient person with the addition of B6. I’m reading the research differently. I see that the immune system is turned on once B6 is given to the person. What I see is an immune response is launched to attack the invader in most of this research. But because the subjects are perceived to be deficient, then instead of seeing the immune system attacking the invader, the researchers are seeing the immune system is turned on to help attack future invaders.
The question becomes even more important once you realize that the leading researcher on the B6 metabolism (Coburn) has suggested in his research the RDA is set to high. His review of the research shows that all the research on determining RDA was done on GROWING rats/mice. He states that a person who has a constant weight and is not growing more muscle needs less B6 than RDA. The point is that if the research is wrong about RDA, then can it be wrong on the value it has set for deficiency?
One of the first pieces of research that we need is for scholars to reevaluate the current literature on B6 deficiency and immunity. Who is determining the deficiency in this research? The second piece of research we need is for an experiment set up to determine the immune response of healthy non-deficient or non-toxic rats who were once given vitamin B6.
See also: Blood Test and B6 Deficiency.