Red Blood Cell Alloantibody Titration - Does the Titration Method Matter?

Background: Red blood cell (RBC) alloantibody titration is a quasi-quantitative method to assess antibody concentration and is considered a useful means of estimating maternal alloimmunization during pregnancy. Traditionally, titration is performed using conventional tube test (CTT). The gel microcolumn agglutination-based method (GMA) has been proven reliable for many immunohematology tests. Our study compared CTT with GMA of two different, commercially available GMA systems for RBC alloantibody titration.

Methods: Serum samples with significant RBC-alloantibodies were evaluated in our study. Each sample was titrated concurrently with CTT, with ID-DiaMed-GmbH, Cressier, Switzerland (GMA1), and with DG Gel Coombs Diagnostic Grifols, Passeig Fluvial, Spain (GMA2).

Results: One hundred thirty-seven titration tests including 50 anti-D, 25 anti-Kell, 10 anti-E, 9 anti-Jka, 8 anti-c, 5 anti-Cw, 5 anti-Fya, 7 anti-M, 6 anti-Kpa, 3 anti-Lua, 1 anti-e, 3 anti-G, and 2 anti-Cha were performed and evaluated. Samples tested by CTT versus GMA1 and GMA2 generated mostly equal or higher titers by GMAs. The results of both comparisons were in good agreement (W = 0.91, p < 0.0001, and W = 0.92, p < 0.0001, respectively). For all antibody specificities, the mean absolute difference in titers ranged from 1 - 3 for both GMA1 and GMA2 versus CTT. Samples tested by GMA1 vs. GMA2 were in almost perfect agreement (W = 0.95, p < 0.0001).

Conclusions: Although both GMAs were found slightly more sensitive than CTT for alloantibody titration, the differences were not significant and the agreement between all methods was very good, possibly indicating GMA as a suitable alternative to CTT in RBC antibody titration.