What is blood crossmatching?

Updated: Jan 22, 2019
  • Author: Ashok Tholpady, MD, MSc; Chief Editor: Jun Teruya, MD, DSc, FCAP  more...
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When blood products are ordered to be administered to a patient who requires transfusion, a series of tests are performed to decrease the risk of an immune-mediated hemolytic reaction caused by incompatible blood.

Hemolytic transfusion reactions occur when the recipient's immune system encounters antigens from donor blood. Antibodies may form in response to these antigens, resulting in destruction of donor red blood cells (RBCs), with sequelae leading to clinical manifestations of fever, hypotension, rigors, acute respiratory failure, and acute renal failure. [1] (Antibody Screening is discussed in a separate article.)

The type and screen are the first pretransfusion compatibility tests performed, and they are used to identify the patient's ABO group and Rh type as well as to detect expected and unexpected antibodies in the patient's serum, respectively. [2]

The crossmatch is the final step of pretransfusion testing as a routine procedure. A portion of donor blood is combined with patient plasma or serum and is checked for agglutination, which would signify incompatible blood. This important step, also known as major crossmatch, serves as the last guard to ensure a safe transfusion. [1]

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