Objectives: Laboratory titration of blood group antibody anti-D is used to monitor immunized pregnancies. A titre of 32 is commonly used to trigger clinical procedures to investigate whether a fetus is suffering complications of haemolytic disease of the fetus and new-born. This so called “trigger titre” is based on historical tube methods. Column agglutination technology (CAT) has largely superseded tube for routine blood group investigations and is used by some laboratories for antibody titration. However, sensitivity differences exist between the two testing platforms and no trigger titre for clinical intervention has been established for column. Furthermore, titres suffer from a lack of reproducibility, produced by many factors including variation in equipment, consumables and techniques of different laboratory scientists. As a consequence, results of studies reporting sensitivity differences between tube and column titres vary widely. In this study, variations were minimised by having one scientist perform titration on the same samples at the same time, in tube and column. The work aims to add to the body of data available on sensitivity differences between CAT and tube for titration of anti-D, with a view to informing a trigger titre for CAT.

Methods: Twenty plasmapheresis donations containing anti-D were titrated under standardised conditions by one individual by indirect antiglobulin technique in tubes and columns. Reproducibility was assessed by titrating a reagent anti-D with each batch of plasmapheresis donations tested.

Results: Column titres of anti-D in plasmapheresis donations were on average 0.8 dilutions higher than tube, showing that column is more sensitive than tube. Reproducibility was high for both techniques, with titre varying ±1 dilution from the mode titre in both tube and column.

Conclusions: Consideration should be given to raising the trigger titre by one dilution when performed by CAT for titration of anti-D. However, it is key that laboratories communicate with clinicians to further evaluate whether the laboratory platform and the trigger titre are appropriate in their local setting.