Based on an observational study of ABO grouping in Gel I reported at the 1997 AABB Annual Meeting, ABO Plasma Grouping discrepancies occurred in 0.8% (26/3183) adult ABO grouping tests in Gel. Anti-B was not detected in 24/26 patients, anti-A was not detected in 2/26 patients, and anti-A1 was not detected in 3183 patients.
In comparison, anti-A and anti-B was detected in 19/26 patients by the immediate-spin tube test, and was detected in 7/26 patients after 10 minute incubation room temperature incubation and centrifugation.
Based on this study and 20 years of gel testing since that time have shown me the anti-A1 is rarely detected in Gel and that 70-80% of ABO plasma grouping discrepancies are resolved using the immediate-spin tube test.
Centrifugation is used quite differently in gel versus tube testing. Centrifugation is used to separate agglutinated cells from un-agglutinated cells within the gel column, but is used to enhance agglutination in standard tube tests by forcing cells together at the bottom of the tube. This may contribute to the increased sensitivity of tube testing in ABO Plasma grouping tests.