Does a Normal Vitamin B12 Level Exclude the Diagnosis of Pernicious Anemia?
Sometimes vitamin B12 levels are found to be normal or elevated in patients in whom you would expect them to be low (or even very low) because Intrinsic Factor Antibodies (IFA) have been detected in the blood test - and these are regarded as diagnostic of Pernicious Anemia. How could this be? Intrinsic Factor Antibodies are found in 40-80% of people with Pernicious Anemia and sometimes they not only bind to natural IF preventing it from binding to vitamin B12, or preventing the B12-IF complex from binding to the B12 receptor, but they can also bind to the reagent IF used in the immunoassays (blood tests) and this can give a falsely elevated result. Sometimes even a B12 level above normal.
There is a trick that the lab can do to deactivate the IF antibodies and when the blood sample is tested again, it will show the true (and often very low) result. So, when a normal or elevated vitamin B12 doesn't seem to fit with the clinical diagnosis of Pernicious Anemia, then other tests can be done, like measuring the MMA (in blood or urine) to determine what the cellular vitamin B12 status is and if elevated, is a much more reliable indicator of deficiency.