Evaluation of a new assay kit for intrinsic factor blocking antibody (type I) as an aid in the diagnosis of pernicious anemia.

Sera from 39 patients with pernicious anemia and 251 patients with various other diseases and 42 healthy normal subjects were tested for intrinsic factor blocking antibody by a Corning commercial kit. Twenty-five (64%) out of 39 pernicious anemia patients showed a positive reaction to the intrinsic factor blocking antibody. The positive incidence of intrinsic factor blocking antibody by this method agreed well with the results obtained in this laboratory over the past 10 years using the charcoal method. No sera from normal subjects tested were positive for the intrinsic factor blocking antibody. All 226 sera with vitamin B12 levels less than 3,500 pg/ml which came from patients without pernicious anemia, were negative for the intrinsic factor blocking antibody. In 15 sera with B12 levels greater than 3,500 pg/ml from patients who received recent B12 medications, 11 sera showed false positive results. On the other hand, no false positive results were obtained by this method in 10 sera with endogenous serum B12 levels greater than 3,500 pg/ml collected from patients with chronic myelogenous leukemia. It is reasonable to presume that this assay is clinically useful for detection of intrinsic factor blocking antibody in the diagnosis of pernicious anemia, if false positive results due to B12 medication are excluded.