The genetic locus for ABO blood type is on the 9th chromosome pair, each pair consists of two single chromosomes, one from the father and the other from the mother, so the blood type is determined by the genes inherited from the parents. It is generally believed that a person’s ABO blood type remains the same for life, but the truth is unexpected. In some pathological states, the ABO blood type can be temporarily changed, and the following are some examples of cases: 1, postpartum hemorrhage patient’s blood type change The patient, female, 26 years old, was hospitalized on November 5, 2008 due to hemorrhage in childbirth, and the blood type was identified at the time of admission: positive and negative stereotypes were AB 3 times, and there was no coagulation on the primary and secondary sides of the cross-matched blood, so the AB RBC suspension was transfused 1000ml, plasma 600ml, no adverse reaction during transfusion. Due to the need for treatment, another blood transfusion was needed on November 13, but the blood type was A type for 3 times. 2. Blood group change in leukemia patient Patient, female, 57 years old, diagnosed with acute myeloid leukemia, blood group identification at the time of transfusion was inconsistent with positive and negative stereotypes, positive stereotype was O and negative stereotype was A. Given a transfusion of 4U of O red blood cells and 6U of machine collected platelets, both red blood cells and platelets were improved and no transfusion reaction occurred. After a period of treatment, he was discharged from the hospital in remission. After the second hospitalization, the blood type was rechecked, and the positive and negative stereotypes matched, and the blood type was A. 3. Blood group change in patients with tumor and anemia The patient, male, 60 years old, was admitted to the hospital for severe anemia, and the blood group was found to be O. 8U of O red blood cells were transfused successively, and there was no transfusion reaction, and the routine red blood cells improved on rechecking. After stabilization, the diagnosis of cardia cancer was confirmed by gastroscopy + biopsy and chemotherapy was given. In the second chemotherapy session, the patient provided the previous hospital records, which showed that the blood type was A. Therefore, the blood type was checked again, and the blood type was A for two times. In fact, not only postpartum hemorrhage, leukemia, tumor and anemia can cause ABO blood group change, but also infection, bone marrow transplantation, chemotherapy, etc. ABO blood group can change temporarily with the disease, and the blood group can be restored after the disease heals or gets better. A review of the papers shows that ABO blood group changes are usually due to the weakening of A antigen or the appearance of acquired B antigen due to disease. The weakening of A antigen is most often seen in leukemia and may be related to the following causes: 1) pathological changes due to abnormal matrix composition of the red blood cell membrane; 2) changes in glycoproteins due to various causes of their glycosyltransferases, resulting in blood group changes. Acquired B antigens are mostly seen in intestinal infections, leading to abnormal proliferation of anaerobic bacteria, which produce enzymes that cut off the amino galactose on the A antigen and turn it into the galactose of the B antigen, thus changing the blood group. For those whose ABO blood type does not match orthotypically with weakened antigen, if the blood type cannot be determined temporarily, if blood transfusion is needed, O type washed red blood cells, AB type plasma and AB type single-collected platelets can be given temporarily, and the same type of blood can be transfused after the blood type is determined [2]; for those whose blood type is changed and whose ABO blood type matches orthotypically, the same type of blood can be transfused with the blood type checked at that time, and it is noted that all blood types need to be checked before transfusion.