Coombs’ crossmatch after negative antibody screening – a retrospective observational study comparing the tube test and the microcolumn technology

Background The antiglobulin crossmatch (AHG XM) is mandatory in Germany and Austria for all patients scheduled for red blood cell (RBC) transfusions. We assessed how many biological relevant RBC alloantibodies are identified by the AHG XM in patients with negative antibody screen (ABS), comparing two screening methods: the conventional tube test (CTT) and the microcolumn technology (MCT). Materials and Methods All AHG XMs performed in the Department of Transfusion Medicine, University Greifswald, were retrospectively analysed for an eight year period. Data source included test results for ABS, AHG XMs and antibody identification. The study period consisted of three parts: (1) 2‐cell ABS and XM by CTT; (2) 2‐cell ABS and XM by MCT; (3) 3‐cells ABS and XM by MCT. Results A total of 312 275 AHG XMs were assessed: 105 647 CTT and 206 628 MCT (after 2‐cell ABS: 80 295 and after 3‐cell ABS 126 333). There was a fivefold increase in reactive AHG XMs using MCT compared to CTT XMs (0·25% vs. 0·05% respectively; P < 0·001). Excluding anti‐A1, other RBC alloantibodies were found with a very low frequency regardless of the method used [CTT 5/105 647 (0·005%), MCT 3/80 295 + 2/126 333 (0·002%); P = 0·3]. RBC alloantibodies were identified in only 1% of the reactive MCT XMs. The two RBC alloantibodies identified after 3‐cell ABS were of minor clinical relevance (anti‐P1, anti‐M). Conclusion When an AHG XM becomes reactive after negative ABS result, this is caused with very few exceptions by clinically irrelevant reactivities. This especially accounts for reactive AHG XM using the MCT.