Wolf,
B12 is the only co-enzyme required for the conversion of methylmalonyl
CoA to succinyl CoA. When B12 is not available, methylmalonyl CoA
(which is quite toxic) is converted to methylmalonic acid. So the
appearance of methylmalonic acid (MMA) is a functional marker for B12
deficiency. MMA was originally measured in the urine because of the
insensitivity of the method, but plasma (so Trevor Walmsley in NZ
assures me) is the specimen of choice.
Perhaps our friends in Sheffield can be a bit more forthcoming about
what they recomend?
Homocysteine is generated by the endogenous de-methylation of
methionine and is catabolised by two pathways - transulphuration to
cysteine (a B6-dependent pathway) and re-methylation to methionine
(which is methylcobalamin and 5-tetrahydromethylfolate-dependent).
There are also various substrate issues in the generation of
homocysteine, but it is not, as such a marker of B12 deficiency,
As for giving B12, Joseph, I hope I get is long before I get into any
grey areas of the reference interval!
Nick Miller
London
2009/7/21 Joseph WATINE <[log in to unmask]>:
> Maybe sometimes a more practical alternative is to give B12 to the patients
> whenever their serum levels of B12 are in the grey zone? (150-300 ng/l)
>
> Dr Joseph Watine, PH, AIHP, PharmD, AAHU, EurClinChem
> Laboratoire de Biologie Polyvalente
> Centre Hospitalier Général
> 12027 Rodez Cedex 9
> France
>
>> Date: Tue, 21 Jul 2009 13:52:55 +0100
>> From: [log in to unmask]
>> Subject: Re: markers for Vit B12 deficiency
>> To: [log in to unmask]
>>
>> Dear all,
>>
>> We have thought about this for a while, and feel that urinary MMA is a
>> good marker. Unfortunately, the 'usual' MMA assays are set up to measure
>> MMA in methylmalonic aciduria patients so may not be sensitive enough
>> for use in Vit B12 deficiency. So we have set up another assay -
>> specifically for use in B12 deficiency investigation here at Sheffield
>> Children's Hospital. We require ~5mL of urine - no need to acidify.
>>
>> Hope this helps, Roy.
>>
>>
>> Dr R Talbot.
>> Clinical Biochemist,
>> Department of Clinical Chemistry,
>> Sheffield Children's Hospital,
>> Western Bank,
>> Sheffield.
>> S10 2TH.
>>
>>
>> >>> Joseph WATINE <[log in to unmask]> 21/7/09 13:41:09 >>>
>>
>> In France, I would rather advise MMA rather than homocysteine
>> measurements because, as far as I know, only MMA measurements are being
>> reimbursed here.
>>
>>
>>
>> Best regards,
>>
>>
>> Dr Joseph Watine, PH, AIHP, PharmD, AAHU, EurClinChem
>> Laboratoire de Biologie Polyvalente
>> Centre Hospitalier Général
>> 12027 Rodez Cedex 9
>> France
>>
>>
>>
>> > Date: Tue, 21 Jul 2009 13:09:58 +0100
>> > From: [log in to unmask]
>> > Subject: markers for Vit B12 deficiency
>> > To: [log in to unmask]
>> >
>> > Dear all,
>> >
>> >
>> > Methyl malonic acid and homocysteine are both markers for B12
>> deficiency. Is there any evidence that we need to measure both? Is one
>> test better than the other? Should MMA be measured in plasma or urine?
>> >
>> > Any advice greatly appreciated.
>> >
>> > Thanks,
>> >
>> > Wolf
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