title: Direct antiglobulin ("Coombs") test-negative autoimmune hemolytic anemia: a review.
abstract: We have reviewed the literature to identify and characterize reports of warm-antibody type, autoimmune hemolytic anemia in which the standard direct antiglobulin reaction was negative but a confirmatory test indicated that the red cells were opsonized with antibody. Three principal reasons account for the absence of a positive direct antiglobulin test in these cases: a) IgG sensitization below the threshold of detection by the commercial antiglobulin reagent, b) low affinity IgG, removed by preparatory washes not conducted at 4°C or at low ionic strength, and c) red cell sensitization by IgA alone, or rarely (monomeric) IgM alone, but not accompanied by complement fixation, and thus not detectable by a commercial antiglobulin reagent that contains anti-IgG and anti-C3. In cases in which the phenotype is compatible with warm-antibody type, autoimmune hemolytic anemia and the direct antiglobulin test is negative, an alternative method to detect low levels of IgG sensitization, use of 4°C, low ionic strength washes to prepare the cells for the direct antiglobulin test reaction to permit retention and identification of low affinity IgG antibodies, and, if the latter are uninformative, testing for sensitization with an anti-IgA, and, if necessary, an anti-IgM reagent identifies cases of warm-antibody type, immune hemolysis not verified by a commercial reagent.
authors.affiliation: Department of Pediatrics, University of Rochester Medical Center, 601 Elmwood Avenue, Rochester, NY 14642-0001, USA; Department of Medicine, 601 Elmwood Avenue, Rochester, NY 14642-0001, USA.
authors.forename: George B
authors.initials: GB
authors.lastname: Segel
authors.affiliation: Department of Medicine, 601 Elmwood Avenue, Rochester, NY 14642-0001, USA. Electronic address: marshall_lichtman@urmc.rochester.edu.
authors.forename: Marshall A
authors.initials: MA
authors.lastname: Lichtman
mesh_terms: D000744:Anemia, Hemolytic, Autoimmune / Q000097:blood* / Q000175:diagnosis* / Q000453:epidemiology; D001323:Autoantibodies / Q000097:blood / Q000276:immunology; D003298:Coombs Test / Q000379:methods / Q000592:standards; D004912:Erythrocytes / Q000276:immunology; D005189:False Positive Reactions; D006461:Hemolysis / Q000276:immunology; D006801:Humans; D015994:Incidence; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
chemical_list: D001323:Autoantibodies
keywords: Antiglobulin test; Autoimmune hemolytic anemia; Cell flow cytometry; Immune hemolytic anemia; Reticulocytosis; Spherocytic hemolytic anemia