de França NG, Poli MC, Ramos PG, Borsoi CS, Colella R States are plasma-incompatible. Also, a small number of institutions prospectively screen group O single donor apheresis PTLs for the presence of high titer agglutinins.(5) Similarly, there is a shortage of identical organ and blood donors. Both situations need blood bank strategies to minimize the biological effects of ABO antibodies. Although, two major challenges in respect to standardized, prospective screening are absence of a recognized reference method and critical end titer that will reasonably differentiate safe from high-titer donors for both clinical settings. According to Brazilian Legislation,(6) it is not mandatory to screen group O blood donors for ABO antibody titrations. The aim of this study was to evaluate agglutinin levels in blood donations. Methods Data collection All blood donor data is confidential in Brazil. Titrations were performed for ABO antibodies in group O donations intended for exsanguinous transfusions in newborns and all group O apheresis donations. Samples of 603 intentional repeat donors were selected for pre-transfusion antibody titration over 9 months. The total number of blood donations from May 2008 until Jan 2009 was 10,967. Titration procedure Diluted sera were incubated in glass tubes at room temperature with a 3% commercial suspension of red blood cells (A1 and B - Diacell, Diamed® Lagoa Santa, Minas Gerais, Brazil). Immediately, after the samples were centrifuged at 3,400 rpm for 15 seconds. Agglutination was considered positive if the red blood cells remained agglutinated after gentle shaking. The highest dilution causing agglutination was assumed to represent IgM antibody titers. By using this semi quantitative technique the anti-A and anti-B were measured and titers higher than 64 were considered high. In these cases, additional information was added on the product label and in the computer system. At the moment of compatibility testing, the system allows only recipient and donor ABO iso groups for the transfusion of packed red blood cells. When possible, our first choice is to stock up to three O blood group units with low titers for exsanguinous transfusion. It is not feasible to follow the same policy with PLT concentrates due to the short period of validity. So our computer system forbids the use of concentrates with high titers in non-identical transfusions. Statistical analysis Descriptive statistics were used to describe the age, gender and anti-A and/or anti-B titers in serum. The sample 260 was corrected for gender and statistical analysis was performed using the Fisher exact and Kruskal-Wallis tests. Results Men were prevalent (7210 - 65.7% male donors) in the donor population of 10,967; correction was done to adjust the frequency distribution. In this period, the titration procedure corresponded to 5.5% of our blood typing routine. The estimates in prevalence for titer results were: anti-A,B < 128 = 86.9% and > 128 = 2.16%; Anti-A > 128 = 9.29% and anti-B > 128 = 4.81%. Table 1 illustrates gender and age distribution for anti- A, anti-B and anti-A,B titer levels. Low mean titers were found in over 50-year-old men for anti-A in comparison with women of the same age (p-value = 0.040). On the other hand, high mean anti-B titers (p-value < 0.001) were observed in young women (19 - 29 years old). High anti-A,B titers (greater than 128) were observed in women of between 30 and 39 years old and those of more than 50 years old (p-value = 0.049). Anti-A,B titers below 32 were found in over 50-year-old men (p-value < 0.001). Interestingly, between 40 and 49 years old there is a different tendency in titer levels for both genders; the lowest mean anti-B titer is for over 30- year-old men and the highest frequency for anti-A > 128 is in over 30-year-old women. Discussion The true biological reason for evolution and phenotypic variations of the ABO antigens and related carbohydrate epitopes remains obscure. ABO antibody levels depend on the ethnic background and environmental factors. In Japan anti-A and anti-B titers decreased over 15 years (1986-2001) and titers of more than 100, as measured using the saline method, are rare. Similar to North Americans, the Japanese population eats more processed food than other Asiatic populations (Laotian and Thai populations).(7) Indeed, lifestyle changes of a group A PLT apheresis donor also explained a report of passively mediated hemolytic transfusion reactions in two different group B recipients.(8) This study shows that our donor population has a predominance of low titers in the studied period even though 13% of titers above 100 were found in São Paulo city. Unfortunately, we do not have data of the location and ethnic background of our donor population, therefore, the reasons that young women have high Anti-B titer levels could not be investigated. We believe that the socioeconomic status and genetic background may explain the results.(9) A comparison between two cities in São Paulo state showed high titers for both men and women with an increase in levels in recent years.(10) The authors did not stratify for age and the technique used for titration was not mentioned. Our titration procedure did not include the determination of IgG titer levels, just IgM. The concern of ABO incompatibility in organ Rev Bras Hematol Hemoter. 2011;33(4):259-62