Failures of cobalamin assays in pernicious anemia.

n engl j med 367;4 nejm.org july 26, 2012 385 Failures of Cobalamin Assays in Pernicious Anemia To the Editor: Cobalamin (vitamin B12) assays have been central to the diagnosis of clinical cobalamin deficiency such as pernicious anemia because the diagnostic sensitivities of older assays have been approximately 95%.1 However, the competitive-binding luminescence assay (CBLA) replaced older microbiologic and radioisotopedilution assays during the past decade. Few studies have compared these methods, and cobalamin CBLA has received less-focused scrutiny than older methods have received in the past. In 2000, a study showing that a CBLA failed to detect many low cobalamin levels2 was disputed by the manufacturer.3 A later article attributed similar