Factors affecting the passive hemagglutination titration: dilution loops, titration trays, vibration, diluents.
Serial dilution with Takatsy loops resulted in exaggerated passive hemagglutination titers with most of the anti-bovine serum albumin sera tested. It appears that certain types of agglutinins adhere to the loop surface and are released only gradually. This adherence, or carry-over effect, was prevented by presoaking loops in gelatin or gelatin-rabbit serum-albumin solutions. Hemolysins did not adhere to loops. In general, hemagglutination reactions performed on plastic trays gave higher titers than those performed in glass test tubes. The quality of the hemagglutination pattern was dependent to a great extent on the type of plastic tray used. As much as a 100-fold difference in titers was obtained depending on the composition of the antiserum diluent. The increase in vibration, in terms of linear displacement (approximately twofold), resulted in an eightfold decrease in titers.