crossmatchingis

Crossmatching is a laboratory procedure used to determine the compatibility of donor and recipient blood before a transfusion. It detects antibodies in the recipient's plasma or serum that could react with donor red blood cells, potentially causing a transfusion reaction. Crossmatching is normally performed after ABO and Rh typing and before administration of red cell units.

There are several crossmatching approaches:

- Immediate spin crossmatch (serologic): donor red cells are mixed with recipient plasma at room temperature to identify immediate agglutination.

- Antiglobulin crossmatch (Coombs crossmatch): uses anti-human globulin to detect clinically significant antibodies that may not react at room temperature.

- Major crossmatch: testing recipient plasma with donor red cells; minor crossmatch (less common) tests donor plasma against recipient red cells.

- Electronic or computer crossmatching: uses patient antibody history and current serology to verify compatibility electronically when no clinically significant antibodies are present.

Purpose and workflow: the aim is to prevent transfusion reactions and alloimmunization by ensuring ABO/Rh compatibility and evaluating clinically significant antibodies. The test is typically part of a broader pretransfusion testing algorithm that may include antibody screening and antigen typing, with units selected accordingly.

In transplantation, crossmatching can also assess donor–recipient compatibility, particularly for HLA antigens. Flow cytometry crossmatch and solid-phase assays are used to predict risk of hyperacute or acute rejection.

Limitations and regulation: a negative crossmatch reduces but does not eliminate risk, as antibodies against non-tested antigens may exist. Emergencies may use uncrossmatched units under approved protocols. Standards are set by organizations such as the AABB, with required quality controls and documentation.