Just wondering if I am misunderstanding the use of the the range for B12.My local health centre has a set range of 150 - 1000. 0.
How does this work?
If someone's level is, say, 155, is this believed to mean that this person is considered to be as well, in B12 terms, as another person who's B12 level is 999?
Simplistic, but I'm genuinely wondering about this.
Simplistically, yes, and no, it doesn't work 😂
The typical way they(*) make ranges is to test a number of healthy people, maybe 200, 500, or a 1000, and see what the distribution is (how many people are at a certain level). They do screen out people with health issues, so it really is supposed to be "healthy" people.
Then they look at that distribution, drop the values/people at either extreme (2.5% of them at either end to be precise), and everything that remains is considered the "normal range."
[This is a bit simplified because they can do some data transformations first if the values are not gaussian distributed, but this is the general idea]
(*) They = The manufacturer of the testing machine/setup will do this, but the blood testing labs themselves can also set their own ranges too - using the same procedure as above - that's why you'll see so many similar but different B12 ranges in the UK.
Here is some info: testing.com/articles/labora...
The trick here is that this is a POPULATION normal range, not YOUR normal range. If we could all have baseline blood tests performed when we're in our early 20s, then we might have a better idea what is actually "normal" for us. This might be more meaningful for autoimmune/other diseases that tend to hit us when we're older... Anyway, "normal" is not "optimal".
FlipperTD will I'm sure give better input if he sees this post - being someone that comes from a lab and all 
I agree if we were tested when well and you d we'd have our personal baseline of b12 level. My first one wax at 57 . Ridiculous when over 50 deemed in at 'at risk 'group.
Not tested at 50+ health check ??
Why???
The screening of the population is the key issue. There's no way that the NHS can do effective screening as there's no central patient records system. B12 ranges will include people who take drugs (e.g. PPI) or have conditions (typically gut conditions or undiagnosed PA)that distort the scale at the bottom of the range, while at the top of the range there might be people who have B12 injections but are not diagnosed with PA because IFAB is inaccurate.
Given this problem the word "normal" should be used cautiously; if someone has low B12 (or Vit D) it should be investigated as low vitamins are typically a sign of ill health.
Testing every person routinely every few years would make sense. The problem is that every test requires a £40 GP appointment to get the test authorised. Until we get routine testing determined by chatGPT where the £40 cost is eliminated, this coupled with statistical misuse of normal distribution will remain a huge problem.
I would also add to jades excellent points that this is geared towards big Pharma also and keeping the range low is desired -they treat fewer people and it's 'cheaper' for them in the short term. Let's not go into the consequences of that policy and the financial burden placed elsewhere as people get ill. Not cheaper at all in fact!
Thank you for this. It's not crystal clear yet but it gives me an idea of the how and why. Very interesting tho.
I think your sceptical understanding / questioning is quite right. 155 is low and should result in a careful exploration of signs and symptoms to consider whether deficiency is present whereas 990 , assuming no supplements are being taken, indicates that no deficiency is present. Ranges are useful if interpreted with nuance.
B12d website
Folate blood test range? 
Checking on my understanding of Folic Acid
Above range Active b12
Folate barely within range 
