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

Summary 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.