Comparison of conventional tube test with diamed gel microcolumn assay for anti-D titration.

Anti-D titration is the first step in the evaluation of the RhD-sensitized patient. Traditionally, anti-D titration has been performed by tube agglutination. Gel microcolumn assay is a method that has gained widespread usage throughout the world, mainly for ABO/Rh typing, unexpected antibody screening and direct antiglobulin tests. As gel assay has become widely used as a routine method to detect red blood cell alloantibodies, a critical anti-D titer needs to be established. Seventy-nine known blood samples with anti-D (titers 1-32) were titrated simultaneously by the conventional tube test and the gel microcolumn assay. Red blood cells (R0r phenotype) were used, with a final concentration of 3% for tube and 0.8% for gel. Serial twofold dilutions (2-2.048) were prepared for each technique, followed by reading in antiglobulin phase. Anti-D titration in the gel microcolumn assay showed significantly higher titers (mean 3.4-fold) than the conventional tube test in all samples studied. Based on these data, it was not possible to determine a critical titer for anti-D titration by the gel microcolumn assay.