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

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.

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 R₂R₂ red blood cells and standardized reagents were utilized.

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).

A tube titer of 8 to 16 correlates with an automated gel titer of 32-128 when R₂R₂ cells are used. Results using the CFA method correlate well with tube and gel analyses.