Background: Reliability of ABO-antibody measurement is important in the context of supplying low-titer ABO incompatible plasma-containing blood products. This study investigated the correlation of anti-A measurements between three different titer methodologies. Methods: Thirty-four blood group O individuals were included. IgM and IgG anti-A was measured by three different methods: (1) manual method (Bio-Rad ID-gel card), (2) automated method (Immucor NEO), (3) flow cytometry (FC) with calibration in molecules of equivalent fluorochrome (MEF). Data were log2 transformed to titer steps (TS) and log2 MEF, respectively. All three methods were benchmarked against the 14/300 WHO anti-A/anti-B standard reagent. Results: The correlation between the manual and automated methods was statistically significant for both IgM (Spearman's rs = 0.89, p <.0001) and IgG (rs = 0.95, p <.0001). The mean TS difference between the manual and automated methods was 0.61 for IgM (p =.0033) and 2.1 for IgG (p <.0001). The manual method yielded IgM titer results that were generally 1 titer step higher than the automated method, whereas for the IgG titrations the difference was generally a median of 2 TS higher. The FC median log2 MEF level was significantly correlated with TS of IgG and IgM for both manual and automated agglutination-based titer methods (0.69 ≤ r2 ≤ 0.91). With the WHO standard reagent, the manual method produced the expected results while the automated method's results were 1 TS lower for both IgM and IgG at all dilutions tested. Conclusion: These results indicate that all three methods are suitable for measuring anti-A in group O whole blood.
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