In this retrospective study, we measured the frequency of unexpected antibodies in the blood. Specific considerations for preoperative preparations were kept in mind for the patients undergoing surgery positive for these antibodies.

After reviewing the results of antibody screening tests lasted for 2 years, the frequency of unexpected antibodies was determined. Surgical patients who were positive for unexpected antibodies were selected and divided into two groups based on their potential need for an intra-operative transfusion (groups with high versus low possibility of transfusion). Blood for the high possibility group was prepared before surgery. For the low possibility group for which preoperative blood preparation was not performed, cases of this group were reviewed whether a blood preparation was delayed or not in case of transfusion.

Among a total 22,463 cases, 340 (1.52%) had positive results for antibody screening tests. Among the 243 patients who were positive for unexpected antibodies, Lewis, Rh, Xga, and mixed antibodies were found in 85, 25, five, and eight cases, respectively. Out of 243 patients, 117 patients, specificities of the unexpected antibodies were not determined and 125 (51.4%) had a history of pregnancy and delivery, and 49 (20.2%) had a history of transfusion. In the low probability group, transfusions were administered for nine patients; transfusion was delayed for two patients due to difficulties with obtaining matched blood.

Patients with unexpected blood antibodies may be at increased risk for delayed transfusion. For rapid transfusion, it might be helpful to keep a record about blood antibodies and introduce a notification system such as medical alert cards. Preoperative blood preparation is needed for timely intraoperative transfusion.