Dear Sir, The prevalence of red blood cell (RBC) alloantibodies among general, hospital-based patients typically has averaged approximately 1% in various studies. The presence of irregular antibodies in healthy voluntary blood donors is uncommon. Anti-M is a fairly common, naturally occurring antibody. Most anti-M are not active at 37 oC and generally are ignored in transfusion practice1. Sometimes, however, they can be clinically significant and become a problem in the immunohaematology laboratory. A male volunteer donor age 32 years donated blood in August 2008. Blood cell grouping showed an “A” positive phenotype, but serum grouping showed a positive reaction (+3) with all the three reagent red cells: A cells, B cells and O cells. The tests were repeated on the ID-Card, DiaClon ABO/D + reverse grouping (gel card) and the same results were observed. When reverse grouping tubes were tested at three different temperatures, 4 oC, 22 oC and 37 oC, for 1 hour, the reaction remained the same at 22 oC and 37 oC but negative at 4 oC. Autocontrols and the direct antiglobuling test were negative. With an antibody screening cell panel, two out of three cells showed positive results and an antibody identification panel (ID-DiaPanel 1-11 by DiaMed, Gmbh 1785 cressier, FR, Switzerland) showed that the suspected antibody was anti-M. The most likely type of antibody was IgG as the plasma was reactive even after treatment with dithiothreitol, which destroys IgM antibodies2. The A1 and O cells used for reverse grouping were shown to be positive for the M antigen. The anti-M present in the sample was interfering in reverse grouping with A1 and O cells. The A1 and O cells treated with papain enzyme gave a negative reaction in reverse grouping, as papain destroys the M antigen. This further confirmed the presence of anti-M with a wide thermal range, reacting at room temperature as well as at 37 oC. The antibody should, therefore, be considered potentially clinically significant. In blood donors, the prevalence of naturally occurring anti-M detectable in microplates with saline suspended cells at room temperature is one in 2,500 with M+N– cells and one in 5,000 with M+N+ cells 3. Some anti-M antibodies are pH-dependent and react at the optimum pH of 6.5. Another feature of this antibody is its failure to react with ficin- or papain-premodified cells. Proteolytic enzymes, such as ficin and papain, cleave the red cell membrane at well-defined sites. Haemolytic disease of newborn, of varying degrees of severity, has been reported in association with anti-M4,5.
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May 1, 2011
P Papay + 9
Open Access