Possible cause of false normal B-12 assays

doi:10.1136/bmj.333.7569.654-c

BMJ 2006;333:654-655 (23 September), doi:10.1136/bmj.333.7569.654-c

Letter

Possible cause of false normal B-12 assays

The first 150 words of the full text of this article appear below.

EDITOR—In response to Devalia,¹ we report a further eightcases of serum samples from patients with megaloblastic anaemiaor subacute combined degeneration of the cord in whom currentassays have failed to detect cobalamin deficiency. The cobalaminresults were well within the manufacturers' reference rangeand not to do with cut-off point. The table shows results fromtwo cases of megaloblastic anaemia, which subsequently respondedto cobalamin treatment, in which pretreatment serum was availablefor analysis by several methods.

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Pretreatment serum cobalamin concentrations in two cases with false normal cobalamin results in current commercial assays

Only two of the five methods found extremely low levels of cobalamindespite severe clinical deficiency. The Bayer centaur assaydetected one of the two case samples as low. These competitivebinding immunoassays are no boil and rely on alkaline hydrolysisand dithiothreitol or monothioglycerol treatment to releasecobalamin from transcobalamin and denature . . . [Full text of this article]

Malcolm S Hamilton, director

United Kingdom External Quality Assessment Scheme, UKNEQAS Haematinics, Department of Haematology, Good Hope NHS Trust, Sutton Coldfield B77 7RR m.s.hamilton@talk21.com

Sheena Blackmore, deputy director, Anne Lee, scheme scientist

United Kingdom External Quality Assessment Scheme, UKNEQAS Haematinics, Department of Haematology, Good Hope NHS Trust, Sutton Coldfield B77 7RR