Objective To investigate the situation of unconformity of positive and reverse ABO blood typ-ing between outpatient and inpatient patients in the hospital,and explore the reasons for unconformity of posi-tive and reverse ABO blood typing detected by microcolumn gel method.Methods A retrospective analysis was conducted on the medical records of totally 425 patients with ABO blood type mismatch who underwent ORTHO VISION Max testing in the hospital from August 2023 to December 2024.Comprehensive analysis was conducted using various methods including the saline tube method,irregular antibody screening,increas-ing plasma volume,4 ℃ enhancement test,absorption elution,and gene sequencing,etc.Results Among 128 192 cases of ABO blood type tests,425 cases showed unconformity of positive and reverse ABO blood typ-ing,accounting for 0.33％.The causes were as follows:antibody weakening in 316 cases(74.35％),bone mar-row transplantation in 40 cases(9.41％),interference from irregular antibodies in 34 cases(8.00％),antigen weakening in 13 cases(3.06％),subgroups in 10 cases(2.35％),cold agglutinins in 6 cases(1.41％),inter-ference from irregular and autoantibodies in 4 cases(0.94％),auto-sensitization of red blood cells in 1 case(0.24％),and other reasons in 1 case(0.24％).Among 316 cases with antibody weakening,239 cases(75.63％)involved type A(anti-B weakening),61 cases(19.30％)involved type B(anti-A weakening),8 ca-ses(2.53％)involved type O(anti-A weakening),6 cases(1.91％)involved type O(anti-B weakening),and 2 cases(0.63％)involved type O(both anti-A and anti-B weakening).In patients with antibody weakening,the disease distribution was mainly cardiovascular disease in 127 cases(40.19％),a history of tumors in 67 ca-ses(21.20％),kidney diseases in 11 cases(3.48％),and orthopedic diseases in 10 cases(3.16％).Conclusion The main reason for the unconformity of positive and reverse ABO blood typing in the hospital is the weakening of the antibodies,especially the predominance of type A(anti-B weakening).Weakened anti-bodies are predominantly in the distribution of cardiovascular disease.For subtype-induced disturbances,a comprehensive analysis combining serology and gene sequencing is recommended.For disease-induced uncon-formity of positive and reverse ABO blood typing,monitoring the patients should be strengthened.