(P-TS-67) Implementation of the BioRad IH-500 Automated Gel Methodology for Measuring Red Cell Antibody Titers

Background/Case Studies:
Determination of red cell antibody titers during pregnancy in patients with a positive antibody screen provides valuable information in the diagnosis and management of hemolytic disease of the fetus and newborn (HDFN). Historically, titers have been performed in test tube with manual pipetting and subjective interpretation of results. This can lead to both intra- and inter-observer variability in the reporting of results. Generally, antibody titers of 16 or greater or an increase of greater than one dilution between visits suggest an increased risk of HDFN. Many institutions consider the presence of maternal anti-K1 a potential risk for HDFN, regardless of the titer. With the advent of automated gel methodology in blood bank testing, multiple vendors have received FDA approval to perform antibody titers in gel. This can significantly reduce the subjectivity of interpreting and reporting results. However, because of the increased sensitivity of performing titers in gel versus test tube, the titer results currently used in diagnosis management of HDFN may need to be adjusted.



We report our experience in validating automated gel testing for red cell antibody titers with a planned implementation in June 2025.

Study

Design/Methods:
75 unique samples with known red cell antibodies were evaluated by both standard test tube methodology and the Bio-Rad IH-500 (Hercules, CA) automated gel platform. The titers of both methodologies were then compared with each other. The following antibodies were evaluated: anti-D, anti-C, anti-c, anti-E, anti-e, anti-K1, anti-Fy^a, anti-Jk^a, anti-Jk^b, Anti-S, anti-s, Anti-M, Anti-N, anti-U and anti-Lu^a. All cells tested were homozygous for the corresponding antigen except for K1. Only heterozygous (K1, K2) cells were available for anti-K1 testing.

Results/Findings:
With the exception of anti-K1, titer results for all red cell antibodies tested in gel were, on average, two dilutions higher than titers in test tube. Titers of anti-K1 were, on average, one dilution higher in gel versus test tube.

Conclusions:
As expected, red cell antibody titers performed in gel were detected at higher dilutions as compared to titers performed in test tube. Using the current accepted titer reference range of 16 or higher for managing potential HDFN, testing in gel could result in unnecessary clinical intervention. A decision has been made at our institution to continue with the current reporting range for six to twelve months. Clinical correlation with the reported titers will then be assessed, and if indicated, the titer reference range for diagnosing possible HDFN can then be adjusted accordingly.