Titers of ABO antibodies in group O blood donors transplantation in some countries such as Sweden(11) and Japan,(12) encouraged the development of more sensitive titration techniques (gel hemagglutination and flow cytometry, respectively). Therefore, this current study, using a simple technique, shows the need of further studies to compare the exact measurement of ABO antibody levels. This is not the first report on ABO antibody distribution in sera from healthy individuals of different age categories. Rieben et al. showed that donor to donor variation did not correlated exactly to age-related changes for all measured parameters. The authors determined isotypes and IgG subclasses of ABO antibodies from sera of 235 Swiss blood donors by enzyme-linked immunosorbent assay (ELISA). Rev Bras Hematol Hemoter. 2011;33(4):259-62 Indeed, they studied titers of up to 40 and found considerable variations between antibody levels by ELISA in different sera with the same agglutination titer. Although the relationship between ABO antibody levels and age of donors based solely on agglutination was first observed in 1929,(13) this is the first study that stratifies Brazilian blood donors by age. A further complexity is that the tests of centers differ in almost every detail, including the use of donor and/or patient plasma or serum, the medium used or dilution, incubation time, centrifugation time and speed, use of polyclonal vs. monoclonal secondary step antibody for indirect agglutination.(9) All these details may affect titer results for transfusions and organ transplants. In a recent review of 261