title: A dual antiglobulin test for the detection of weak or nonagglutinating immunoglobulin M warm autoantibodies.
abstract: BACKGROUND
  Immunoglobulin (Ig)M warm autoantibodies (AABs) usually cause severe autoimmune hemolytic anemia (AIHA) and, in some cases, red blood cell (RBC)-bound IgM cannot be detected. We describe a simple dual antiglobulin test (DDAT) for diagnosing such cases.
  
  
  METHODS
  A patient with erroneously suspected cold agglutinin syndrome was investigated. The direct antiglobulin test (DAT) was performed using standard techniques and dual (two stages) antiglobulin reagents (IgG rabbit anti-human IgM, IgG goat anti-rabbit IgG).
  
  
  RESULTS
  A cold agglutinin syndrome was diagnosed initially, as the patient's serum was reactive with RBCs at a temperature of 28 degrees C or less, and the DAT was strongly positive with anti-C(3)d. Six months later, the patient was reexamined at this hospital due to progressive hemolysis. His RBCs were found to be coated with IgM warm AABs that only became detectable using a DDAT, and his serum contained only a weak cold agglutinin. The hemolysis remained refractory to treatment with prednisolone and also prednisolone plus azathioprine, but gradually improved after treatment with prednisolone plus cyclophosphamide.
  
  
  CONCLUSIONS
  Weak or nonagglutinating RBC-bound IgM warm antibodies can be identified by the presented DDAT.
authors.affiliation: Institute for Transfusion Medicine, Charité-University Medicine, Berlin, Germany.
authors.forename: Thilo
authors.initials: T
authors.lastname: Bartolmäs
authors.forename: Abdulgabar
authors.initials: A
authors.lastname: Salama
mesh_terms: D000328:Adult; D000744:Anemia, Hemolytic, Autoimmune / Q000188:drug therapy / Q000276:immunology*; D001323:Autoantibodies / Q000097:blood*; D003298:Coombs Test / Q000379:methods*; D006801:Humans; D007075:Immunoglobulin M / Q000097:blood*; D008297:Male
chemical_list: D001323:Autoantibodies; D007075:Immunoglobulin M