D‐Alloantibody Titration Assessment Study: In Search of a Common Antibody Titration Platform—A BEST Collaborative Study

Background Alloimmunization against D‐antigen can cause severe Hemolytic Disease of the Fetus and Newborn (HDFN). Traditionally, anti‐D‐titers are measured using a saline indirect antiglobulin test (tube testing). Anti‐D‐titers ≥8 during pregnancy trigger an escalation in maternal care. Tube testing is labor‐intensive and known for imprecision. Automated gel‐based titration is more sensitive and precise than tube titration for the detection of anti‐D. A gel titer correlated with potential fetal anemia has not been established, as studies comparing gel and tube titers provide widely variable results. This multicenter study tested anti‐D samples in parallel to characterize the difference in sensitivity between tube and automated gel assays. Study Design and Methods Patients alloimmunized to RhD had samples tested using tube and automated gel titration methods. A total of 647 samples were tested in parallel. A subset of 141 samples also had anti‐D levels quantified using continuous flow analysis (CFA). Controlled lots of R 2 R 2 red blood cells and standardized reagents were utilized. Results Results demonstrated that gel‐based methods yielded mean titers 2.5–3 dilutions higher than tube; this difference diminished at tube titers >128. Notably, several samples previously considered negative by tube were positive by gel. Anti‐D levels quantified by CFA demonstrated a good correlation with tube and gel testing ( R = 0.75–0.9 for tube; R = 0.85–0.89 for gel). Discussion A tube titer of 8 to 16 correlates with an automated gel titer of 32–128 when R 2 R 2 cells are used. Results using the CFA method correlate well with tube and gel analyses.