(151) A comparison of techniques for antibody titers in screening for hemolytic disease of the fetus

To compare the relationship between titer concentrations via gel microcolumn agglutination (GMA) and conventional tube testing (CTT) methods to examine if critical titer thresholds should differ between the two techniques. 

Study Design:

Retrospective chart review on all obstetric patients treated at a single tertiary care center with RBC antibodies from November 2018 to October 2022. Patients were included in the statistical analysis if there were parallel CTT and GMA titration studies available. GMA vs CTT titers were graphed via bubble plots, and polynomial regression analysis was used to evaluate the correlation between the two methods. Logistical regression was used to evaluate the sensitivity and specificity of GMA titers for prediction of a critical CTT titer of 16.

Results:

166 GMA titers from 87 patients had corresponding CTT titers. The most common antibody was anti-Rh(D) (76) followed by anti-Kell (29). Polynomial regression indicated a relationship between GMA titers and CTT titers (R2 = 0.5325, p < 0.001). The relationship changed significantly with removal of anti-Kell antibodies (R2 = 0.6733, p < 0.001).  GMA titers were predictive of a critical CTT (AUC 0.97, p< 0.001) for non-anti-Kell antibodies but not predictive for anti-Kell antibodies (p = 0.134). Overall a GMA titer of 64 was predictive of a CTT titer of 16 or higher with 90.7% (95% CI 82.5-95.9%) sensitivity and 85.0% (95% CI 75.3-92.0%) specificity (Table 2). All GMA results of 32 or higher for anti-Kell antibodies had CTT of at least 16, whereas the same could not be said of the non-anti-Kell antibodies until GMA titers reached at least 512. 

Conclusion:

There is a correlation between GMA and CTT titers. GMA titers are consistently higher than CTT titers in all antibodies tested in our study except for anti-Kell. A predictive table was created for provider reference if their hospital’s blood bank only employs GMA techniques.