Fasting before blood tests?

[Cathyjw]

Hi,

Just a quick question are you supposed to fast before b12 and folate blood tests?

Also have many people tested negative for gastric parietal cells but positive for intrinsic factor?

Thanks

[Gambit62 Administrator]

a) fasting isn't necessary with B12

b) some suggest fasting with folate as it isn't a stored vitamin so is quite responsive to amounts that you have recently ingested ... but not sure entirely of the logic of fasting.

c) yes you can test negative for GPCA but positive for IFA. You can a get a false positive for IFA if you have supplemented B12 just be fore the test - how long before the test counts as 'just' depends on the assay metnod but could be as much as 2 weeks. However, is also genuinely possible to be negative on GPCA but postive for IFA.

[fbirder]

You can test negative for antiGPC antibodies and positive for antiIF, but it is unlikely.

The BCSH - onlinelibrary.wiley.com/doi... - say that antiGPC is found in 80% of people with PA and that 95% of people who test positive for antiIF have PA.

So, all other things being equal, the chances of being antiGPC negative and antiIF positive are less than 1%.