Re: "Perhaps our friends in Sheffield can be a bit more forthcoming
about
what they recommend?"
Not quite sure what you mean - from our experience the assays that
measure methylmalonic acid are not sufficiently sensitive enough to
measure the low concentrations seen in B12 deficiency, whereas our assay
is, as I previously said, set up to specifically measure these low
concentrations. We use urinary MMA measurement mainly as it is
non-invasive, but have no experience of plasma MMA assays - perhaps
Trevor Walmsley would like to comment?
Roy.
>>> Nick Miller <[log in to unmask]> 21/7/09 15:12:09 >>>
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 recommend?
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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