Abstract: Objective To share the blood group identification and analysis process of a patient whose ABO blood type does not match the positive and negative typing, so as to improve the recognition and processing ability of the clinical laboratory on difficult blood types and ensure the safety of clinical blood use. Methods The blood samples were collected from a patient whose ABO blood group did not match the positive and negative types in the Department of Critical Care Medicine of Guiyang Second Hospital. Serological test and gene detection were used to identify the ABO blood group of the patient. Results The positive type of ABO blood group in patient samples is B type and the negative type is AB type. Irregular antibody screening direct anti-human globulin test and indirect anti-human globulin test were negative. Absorption-emission test suggested that red blood cells contained A antigen PCR gene amplification and sequencing showed that the genotype of ABO*A1.02 and ABO*B.01 was A1/B type and A1B type; ABO gene mutations in exon 6 297A>G and exon 7 467C>T, 526C>G, 657C>T, 703G>A, 796C>A, 803G>C, 874C>G, 930G>A of the ABO gene have not been recorded in the International Blood Transfusion Association. Conclusion The ABO blood group of the patient was finally determined as A1B by serological test and molecular biological technology. The 874C>G gene mutation on the patient's exon 7 may be a new discovery revealed by this study for the first time. Gene site mutation interferes with the correct identification of blood type, and the combination of serological tests and molecular biology technology is of great significance for the correct identification of blood type and ensuring clinical safe blood transfusion treatment.

Key words: blood type, ABO blood group, difficult blood type, serological test, molecular biology technology, gene mutation