Background  There are various factors that affect the identification of ABO blood type, and correct identification of ABO blood type is very important for ensuring the safety of blood transfusion.

  Objective  To investigate the clinical features of ABO typing discrepancy and related influencing factors.

  Methods  From January 2017 to December 2019, clinical data and blood types were collected from the patients with ABO typing discrepancy who were tested in the medical laboratory center, the First Medical Center of Chinese PLA General Hospital, and the patients without ABO typing discrepancy were enrolled as controls. The distribution frequency of blood types, influencing factors, and clinical features were analyzed for the patients with ABO typing discrepancy.

  Results  A total of 132 patients with ABO typing discrepancy were enrolled, among whom there were 75 males and 57 females, with an average age of (50.3 ± 19.3) years (range, 3-84 years). Of all patients, 89 (67.42%) cases had a history of surgery and 23 (17.42%) cases had a history of blood transfusion. There were 142 patients in the control group (79 males and 63 females), aged 10-78 (50.5 ± 15.55) years, among whom 68 (47.88%) cases had a history of surgery and 2 (1.40%) cases had a history of blood transfusion. As for the blood types with discrepancy, 59 patients (44.7%) were type B, 38 (28.8%) were type A, 28 (21.2%) were type AB, and 7 (5.3%) were type O. The blood types with discrepancy were observed in 21 clinical departments, with 21 patients (15.9%) in department of hematology, 15 (11.36%) in department of bone surgery, 14 (10.6%) in department of hepatobiliary surgery, 11 (8.33%) in department of general surgery, and 11 (8.33%) in department of vascular medicine or vascular surgery, with a proportion of < 5% for other departments. For the patients with ABO typing discrepancy, low/weak affinity antibody A accounted for 3.79%, low/weak affinity antibody B accounted for 18.18%, weak A antigen accounted for 3.03%, weak B antigen accounted for 12.12%, hematopoietic stem cell transplantation accounted for 10.60%, irregular antibody accounted for 46.70%, subtype accounted for 3.79%, and cold agglutination accounted for 1.51%. The diseases of patients with ABO typing discrepancy mainly included blood diseases, tumors, gastrointestinal bleeding, hepatobiliary inflammation, valvular heart disease, hypoproteinemia, nephrotic syndrome, and osteoarthritis. The binary logistic regression analysis showed that blood diseases, tumors, history of surgery, and history of blood transfusion were associated with ABO typing discrepancy.

  Conclusion  It is possible that the antibody of ABO blood group system can not be detected during blood typing. Blood diseases, tumors, history of surgery, and history of blood transfusion are the main influencing factors for ABO typing discrepancy. Serological methods should be used in combination with clinical data to determine the correct blood type.