Abstract: Objective A prospective multi-center study was conducted to investigate the correlation between agglutination intensity of Anti-A/B antibody and age in infants <1 year of age. Methods 1 564 infants were divided into 12 groups by age. The ABO reverse typing was respectively detected by tube method at room temperature and at 4℃ and microcolumn gel method. Results Considering the results of reverse typing by tube method at 4 ℃ and microcolumn gel method, it showed that agglutination score ≥ 4 points （agglutination ≥ 1^+W） in the infants age ≥6 months and that agglutination score ≥7 points （agglutination ≥2^+W） in the infants age ≥ 9 months. Considering the results of reverse grouping by test tube method at room temperature, it showed that the agglutination score ≥4 points （agglutination ≥1^+W） in the infants age ≥ 8 months, and that the agglutination score ≥7 points （agglutination ≥2^+W） in the infants age ≥ 10 months. In addition, the agglutination scores （A cell and B cell） of group O infants at 1-month old were higher than group B infants （A cells） and group A infants （B cell） respectively in reverse grouping. In regards of group O infants, the agglutination scores of A cells and B cells reached to the nadir at the age of 4 months, then gradually increased. Conclusion We recommended the detection time and agglutination intensity value of ABO reverse typing in Chinese infants within 1 year old.

Key words: Infant, ABO blood group, Reverse typing, Antibody