Methods for detecting RBC agglutination

Agglutination can be scored by various methods; the degree of agglutination generally correlates with the concentration of the anti-RBC antibody. (A) In the tube method, agglutination is assessed following resuspension of RBCs and is graded according to a visual scale, with complete resuspension of cells (no agglutination) scored as "0" and complete lack of resuspension (greatest agglutination) scored as "4". (B) In the solid phase method, patient plasma and indicator RBCs are added to a microwell plate that is pre-coated with RBC membranes containing antigen. Greater adhesion along the entire well correlates with greater agglutination. (C) In the column method, agglutinated cells are retained in the column, whereas unagglutinated cells pellet at the bottom of the tube. Results can be read by an automated system. Refer to UpToDate topics on pretransfusion testing for further information.