Pernicious Anaemia Society
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B12 deficiency and MCV values?

Hi, I have been self medicating for a B12 deficiency for around 10 months (was 254 before I started) with reasonable success (Jarrow B12 5000mcg sub lingual tablets plus spray and Thorne B complex). My neurological symptoms have receded, still have some balance ataxia, but the main symptom I still seem to have is breathlessness. My MCV was 96 when last measured 12 months ago - is this high? Can one still be breathless due to B12 deficiency without MCV being out of range?

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whilst macrocytic anaemia is one way that B12 deficiency causes breathlessness it isn't the only possibilty - another possibility is the effects on the nervous system - in particularly disruption to the autonomic system which can result in the brain mis-interpreting signals that it uses to control things like breathing - so it thinks that your oxygen is low when it isn't and you start breathing more heavily to compensate.

If you have been improving for 10 months then any macrocytosis should have gone - it clears as old red blood cells die and are replaced by new ones - which takes about 4 months.

From memory of the most common ranges think that 96 is actually towards the middle of the range for MCV. If you have a copy of your results then that will include the range.

Having an absorption problem that lead to a B12 deficiency can result in other deficiencies eg iron and folate.

Basically MCV is one indicator in a series of clues - and trying to solve things using just one clue is a guess at best.


Thanks, very useful. The limit for MCV on my blood test was shown as 78 - 98


in that case its at the high end, so tending towards macrocytosis 12 months ago - would expect it to be much lower if test was repeated now

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