Frequency and specificity of red blood cells alloantibodies in routine pretransfusion processing Objectives: Examine the specificity and frequency of alloantibodies against erythrocyte antigens in routine pretransfusion testing. Study Design: Cross-sectional study based on historical data. Material and Methods: The materials of this research are the data available from the Department of Transfusion Medicine's historical data, General County Hospital Vinkovci. The data used for this research were collected in the period between January 2016 and December 2020. The methods of immunohematological tests were conducted with Wadiana, Grifols analyzer and by manual method using ID-Card LISS/Coombs mycrocards. Results: Of the total 27 626 tested blood types, 238 had positive IAT result (0,86 %), of which 70,2 % were of female gender. The smallest share of patients is in the age group of up to 30 years of age, among which the most common antibody is anti-M. The largest share of patients is in the age groups of 50 to 95 years of age, among which the anti-D antibody is the most common. Anti-D antibody is most commonly confirmed in bloodtype A, AB and O, and in 71 % of RhD negative patients. Anti-M is confirmed in 27,8 % of pregnant women. Antibodies with the most common frequency are anti-D (28,6 %), anti-E (17,2 %), anti-K (15,3 %), anti-M (10,3 %). Conclusion: Alloantibody frequency in routine pretransfusion testing is around 1 %, and the most common confirmed antibody is anti-D. The differences in frequency and specificity of antibodies depending on gender were not detected, while depending on age there is a statistically significant difference. There is an interconnection between anti-D antibody and age groups of 50 to 95 years of age. According to anamnestic data, anti-D, anti-K and anti-E antibodies can be linked with previous transfusions, while anti-M antibody can be linked with previous pregnancies.