Prewarm technique

Prewarm technique can be used to prevent cold-reactive alloantibodies or autoantibodies from reacting in the IAT phase. Specifically, prewarm technique prevents cold antibodies from binding complement at RT (as opposed to 37^o C ) and subsequently being detected by anti-C3 in the IAT by polyspecific AHG serum. This assumes that pretransfusion testing is done

• using clotted specimens (C1qrs requires free Ca⁺⁺ ions; EDTA, for example, chelates Ca⁺⁺ and stops complement binding at C1q)

• using polyspecific AHG containing both anti-IgG and anti-C3.

If these pretransfusion test conditions apply, an antibody-antigen reaction occurring at RT, before tests are incubated at 37^o C can be detected in the IAT phase. What happens is that the antibody reacts at RT and binds complement to C3. The clinically insignificant cold antibodies then elute off the red cells at 37^o C , but any C3 bound at RT will remain on the cells and be detected by the anti-C3 in polyspecific AHG serum.

Prewarm technique is somewhat controversial (see Controversies), because some transfusion services use it to determine the clinical significance of antibodies, something that it was never intended to do.

Method

The prewarm method is briefly outlined below. A detailed method can be found in the AABB Technical Manual and similar references.

1. Prewarm serum and red cells to 37^o C for approximately 10 minutes prior to doing the pretransfusion test.

2. Also prewarm a bottle of saline and a pipette to 37^o C .

3. Add serum to cells using a prewarmed pipette.

4. Ensure that the tests remain at 37^o C before they are read. This includes washing the antiglobulin tests using saline prewarmed to 37^o C and using a centrifuge kept inside a 37^o C dry-air incubator.

Clinical Significance

Prewarm Technique

Controversies