title: Paradoxical findings in direct antiglobulin test and classification of agglutinating autoantibodies using eluates and monospecific anti-human globulin sera.
abstract: OBJECTIVE
  Agglutinating autoantibodies are rarely the cause of autoimmune haemolytic anaemia (AIHA) of warm type. These antibodies can be difficult to classify, and serological testing may result in confusion. Here, we describe the occurrence of paradoxical results in direct antiglobulin test (DAT) and a simple technique for the characterization of such antibodies.
  
  
  METHODS
  Seven patients with AIHA were included in this study. Serological testing was performed using standard techniques. Classification of autoantibodies was performed by preincubation of the eluates from patients' red blood cells (RBCs) with monospecific anti-human globulin sera (mAHG).
  
  
  RESULTS
  Strong autoagglutination of patients' RBCs was observed in six of seven cases, with the identification of panagglutinating serum antibodies in three patients. Initially, cold agglutinins with high thermal amplitude were suggested in four patients, and IgM warm autoantibodies were suggested in the remaining three patients. However, inhibition of the eluates revealed autoantibodies of IgA class in two patients, of IgM class in three other cases and of IgG class in two patients. The results of DAT were confusing due to paradoxical effects of mAHG and/or strong autoagglutination.
  
  
  CONCLUSIONS
  Strongly agglutinating autoantibodies can be a source of confusion and can be classified by inhibition experiments using eluates and monospecific antibodies.
authors.affiliation: Institut für Transfusionsmedizin, Charité-Universitätsmedizin Berlin, Berlin, Germany.
authors.forename: T
authors.initials: T
authors.lastname: Bartolmäs
authors.forename: B
authors.initials: B
authors.lastname: Mayer
authors.forename: S
authors.initials: S
authors.lastname: Yürek
authors.forename: R
authors.initials: R
authors.lastname: Genth
authors.forename: A
authors.initials: A
authors.lastname: Salama
mesh_terms: D000744:Anemia, Hemolytic, Autoimmune / Q000097:blood* / Q000276:immunology; D001323:Autoantibodies / Q000097:blood / Q000276:immunology*; D003298:Coombs Test / Q000592:standards*; D003450:Cryoglobulins / Q000276:immunology; D004912:Erythrocytes / Q000276:immunology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012680:Sensitivity and Specificity
chemical_list: D001323:Autoantibodies; D003450:Cryoglobulins; C029443:cold agglutinins
keywords: RBC antigens and antibodies; antibody - function; immunoglobulins; immunohaematology; serological testing