In the immediate spin method, two drops of patient serum are tested against a drop of 3–5% suspension of donor cells in a test tube and spun in a serofuge. Agglutination or hemolysis (i.e., positive Coombs test) in the test tube is a positive reaction and the unit should not be transfused. If an antibody is suspected, potential donor units must first be screened for the corresponding antigen by phenotyping them. Antigen negative units are then tested against the patient plasma using an antiglobulin/indirect crossmatch technique at 37 degrees Celsius to enhance reactivity and make the test easier to read. In urgent cases where crossmatching cannot be completed, and the risk of dropping hemoglobin outweighs the risk of transfusing uncrossmatched blood, O-negative blood is used, followed by crossmatch as soon as possible. O-negative is also used for children and women of childbearing age. It is preferable for the laboratory to obtain a pre-transfusion sample in these cases so a type and screen can be performed to determine the actual blood group of the patient and to check for alloantibodies. Compatibility of ABO and Rh system for Red Cell (Erythrocyte) Transfusion
This chart shows possible matches in blood transfusion between donor and receiver using ABO and Rh system. Adverse effects
In the same way that the safety of pharmaceutical products is overseen by pharmacovigilance, the safety of blood and blood products is overseen by haemovigilance.
Fournier gangrene is a type of necrotizing fasciitis or gangrene affecting the external genitalia or perineum. It commonly occurs in older men, but it
can also occur in women and children. It is more likely to occur in diabetics, alcoholics, or those who are immunocompromised. About one per 62,500 males are affected per year. Males are affected about 40 times more often than females. It was first described by Baurienne in 1764 and is named after a French venereologist, Jean Alfred Fournier, following five cases he presented in clinical lectures in 1883. Signs and symptoms
Initial symptoms of Fournier gangrene include swelling or sudden pain in the scrotum, fever, pallor, and generalized weakness. It is characterized by pain that extends beyond the border of the demarcated erythema. Most cases present mildly, but can progress in hours. Subcutaneous air is often one of the specific clinical signs, but is not seen in >50% of presenting clinical cases. More marked cases are characterized by a foul odor and necrotic infected tissue. Crepitus has been reported. It begins as a subcutaneous infection. However,  necrotic patches soon appear in the overlying skin, which later develop into necrosis. Cause
Most cases of Fournier gangrene are infected with both aerobic and anaerobic bacteria such as Clostridium perfringens. It can also result from infections caused by group A streptococcus (GAS), as well as other pathogens such as Staphylococcus aureus and Vibrio vulnificus.