Pernicious Anaemia Society
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Pmol pg ng etc ...... importance of giving detailed blood levels


There's a big difference in results posted in pmol compared to pg for example but people keep posting numbers without clarifying which measurement was used.

I've noticed it quite a lot recently with people's b12 and vit d results on here.

It causes confusion and worries others too when someone says they were really low/high and we then think ours could be bad too.

It's a shame there isn't just one standard measurement but there isn't so please post the number and the measurement 😀

Then I'll be able to sleep tonight lol

Thank you

5 Replies

My two most recent tests came back in different measurements. The first in pg but the second in pmol/l so I had to convert to get a proper comparison.

The printout said 666pmol/l but that converts to 902.4pg/ml.

That's quite a difference number wise.

With vit d the difference is something like 2.5x

That's quite a bit when someone just quotes or is just told a number by a gp etc.


We chemists have been using moles for decades. But medics are really biologists and they like using strange units and terminology. But they're slowly coming around to using sensible measures.

Who knows what will happen post-Brexit though. I've already heard calls for a return to imperial weights so don't be surprised to find results reported in grains per jeroboam.


We regularly see confusion about moles and mass over in the thyroid lot.

T4 is converted to T3 by removal of one iodine atom. But we tend to think of, say, 100 micrograms of T4 being converted into 100 micrograms of T3 - when it is more like 80 (can't remember the exact number and it doesn't matter for discussion). It can look as if 20 micrograms isn't accounted for.

Thinking of it all in molar terms should remove that confusion. (Thought probably add lots of other issues.)

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I have a chemistry background as well and I agree, it makes much more sense to use moles. The confusion occurs when some countries like Australia use moles (actually pmol/L, picomoles) and others like the US and UK use grams (pg/mL or ng/L which are equivalent). It is important to include the units with your numbers when you post them here.

There are web sites that can do the conversion for you. Google "convert B12 unit conversion" for instance.


Thankfully, for things like the Free T4 test, the units end up with ranges that are quite distinctive.

0.7 to 1.4 ng/dL

9 to 18 pmol/L

B12 results are close enough to confuse, and different enough to potentially be a problem.


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