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Flow-cytometric quantitation of anti-D antibodies
J O Hildén1, K Backteman, J Nilsson
1Department of Transfusion Medicine and Clinical Immunology, University Hospital, Linköping, Sweden.
Objectives:
Quantitation of Rh antibodies is important clinically in predicting the risk of hemolytic disease of the newborn. We describe a flow cytometry method for the quantitation of anti-D antibodies that we developed in parallel to a recently described method.
Methods:
As a secondary antibody we used whole IgG instead of Fab molecules. The advantages, besides lower cost, include a strong fluorescence signal with no need for amplification, and the possibility of diluting samples to minimize the risk of agglutination by IgM antibodies. We did extensive studies on reproducibility.
Results:
Reproducibility was superior to the autoanalyzer method. The two methods were roughly in agreement in estimating low, medium, or high levels of anti-D with a correlation coefficient of 0.89. The autoanalyzer measures the in vitro agglutination of all anti-D antibodies whereas flow cytometry measures the amount of IgG anti-D bound to red cells, which is more like the in vivo situation.
Conclusion:
Further studies in a clinical setting will show whether flow-cytometric quantitation may improve the diagnostic value of anti-D concentration measurement.