The common name for various manufacturers’ versions of “column agglutination” testing. Gel testing occurs in small columns filled with a viscous gel. The RBCs and plasma being tested are added to the chamber at the top of the column and incubated, followed by centrifugation to try to force the RBCs through the gel to the bottom of the column. Gel makes positive reactions obvious (usually) in two ways: First, RBCs that are agglutinated will be stopped earlier in the gel than those that are not agglutinated. Second, the gel (when performing an antibody screening test) contains anti-IgG, which binds to the IgG coating RBCs in positive reactions, and further inhibits transport of the RBCs through the gel.