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Potential pitfall in diagnosing pernicious anemia.

In 2 women with pernicious anemia (diagnosed by bone marrow aspiration, elevated serum levels of homocysteine and methylmalonic acid, and positive clinical response to vitamin B12 therapy), pretreatment serum vitamin B12 levels (determined by an automated analyzer) were above normal. Both patients had circulating intrinsic factor-blocking antibodies. Such antibodies are present in up to 70% of patients with pernicious anemia; these antibodies may interfere with automated laboratory assays for serum vitamin B12, which utilize a method based on the competitive binding of serum vitamin B12 to reagent intrinsic factor. Manufacturers of automated vitamin B12 assays recommend that patients be tested for intrinsic factor antibodies if test results for serum vitamin B12 conflict with the clinical diagnosis.

Comment: Failure to diagnose and treat pernicious anemia in a timely fashion can lead to permanent neurological impairment. Therefore, when measuring serum vitamin B12 levels, it is essential that the practitioner be aware of the laboratory method that is being used. If the laboratory is using the type of automated assay described above, it may also be necessary to measure intrinsic factor-blocking antibodies. However, considering the high cost of that test ($94 according to one lab), it might be more cost effective to measure serum vitamin B12 by a method that does not give incorrect results in patients who have intrinsic factor-blocking antibodies.

Yang DT, Cook 12J. Spurious elevations of vitamin 812 with pernicious anemia, N Fogl I Med, 2012;366:1742-1743.

by Alan R. Gaby, MD

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Title Annotation:Literature Review & Commentary
Author:Gaby, Alan R.
Publication:Townsend Letter
Article Type:Brief article
Geographic Code:1USA
Date:Oct 1, 2012
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