The distribution of the demographic data revealed that the age group of 21C40?years had the most frequent unexpected antibodies (45%) while female participants had a higher number (77%) than the males. must be followed during the transfusion of blood to individuals with these medical conditions. Keywords: Unpredicted antibody, Blood group, Blood transfusion 1.?Intro Blood compatibility screening is necessary to prevent critical complications during blood transfusion. The American Association of Blood Banks (AABB) offers recommended that ABO typing, Rh typing, unpredicted antibody screening, and cross-matching must be performed before a blood transfusion. Since blood antibody screening is generally included in the list of preoperative checks, an emergency transfusion can be performed immediately in the case of massive intraoperative bleeding. However, when an emergency transfusion is required in circumstances in which the unpredicted antibody screening test has not been performed, the delay in finding compatible blood may be life-threatening (Kim et al., 2013). Unpredicted antibodies, also called irregular antibodies, cannot be confirmed to exist in a person’s serum until it is tested. They include antibodies and antigens from systems such as Rh, MNSs, Duffy, and Kidd (Mazonson et al., 2014). Unpredicted antibodies have quite a major impact since they can cause severe transfusion reactions such as acute or delayed hemolytic transfusion reaction or neonate hemolytic syndrome. Blood grouping and cross-matching is one of the most important checks to Scutellarein conduct before blood transfusion. Therefore, proper knowledge of the blood group system, its medical significance, typing and cross-matching methods, and experience is vital in the prevention of transfusion-related complications (Getshen et al., 2019). Furthermore, knowledge of the blood group system is required to tackle diseases linked to blood group (Mazonson et al., 2014). RBC alloantibody formation is definitely uncertain in individuals who have previously been transfused or Scutellarein pregnant. Further, the alloimmunization rate has Scutellarein been recorded to be 1C10% and even higher (20%) in regularly transfused populations (sickle cell disease or thalassemia individuals). Pre-transfusion screening, particularly antibody screening, has been developed to identify these antibodies, and antibody detection (ABI) techniques are designed to detect different antibodies (Goss et al., 2016). This study aims to determine the event of unpredicted antibodies in Saudi individuals prior to blood transfusion and to study their association with several medical conditions. 2.?Materials and methods This prospective cross-sectional study was conducted among hospitalized individuals needing blood transfusions from June 2019 to June 2020. 2.1. Inclusion criteria No matter sex and age, only Saudi individuals who have been hospitalized for blood transfusion were included in this study. 2.2. Exclusion criteria Patients who have a history of hematological malignancies were excluded. A total of 9764 blood samples were obtained. The designed questionnaire was utilized for the collection of demographic and medical data by a well-trained data collection team. All the following techniques were verified by hematology and blood banking experts according to the standard procedures operation manual. 2.3. ABO and Rh grouping ABO and Rh typing should be carried out for the blood of both the donor and the recipient. ABO typing is performed by screening RBCs with anti-A and anti-B antisera and A1 and B serum. Rh type is determined with the anti-Rh, anti-D; if the donors initial anti-D blood test result Scutellarein is definitely negative, then the blood is screened using a fragile D (Du) detection method. If an Rh test result is definitely positive, the SEMA3A blood samples label will go through Rh positive (AABB, 1993) (Bio-Rad Laboratories, Inc.). 2.4. Antibody screening test The individuals serum or plasma should be screened for any single-donor suspension of unpooled RBC group O reagent. This is in compliance with AABB Requirements (AABB, 1993). Such reagent cells are chosen because they carry the blood group antigens required for the recognition of the most clinically important RBC alloantibodies, i.e., those antibodies reactive at 37?C in the AHG.