The titration of tetanus antitoxin V. Effect of formalization method for the fixation of sheep erythrocytes on the indirect haemagglutination test

Two methods of fixation of sheep erythrocytes with formaldehyde for the titration of tetanus antitoxin by the indirect haemagglutination (IHA) test have been compared. The cells fixed with 3% formaldehyde at 4-8 degrees C for 24 h (formaldehyde (I) fixed cells) were less sensitive than the cells fixed with 3% formaldehyde at 4-8 degrees C for 24 h and subsequently treated with 40% formaldehyde at 4-8 degrees C for a further 24 h (formaldehyde (II) fixed cells). The correlation between the toxin neutralization (TN) and IHA titres using formaldehyde (I) fixed cells was better than that obtained with formaldehyde (II) fixed cells. There was no statistically significant difference between TN and IHA titres after treatment of the sera with 2-Mercaptoethanol using formaldehyde (I) fixed cells. Formaldehyde (I) fixed cells can be used for two months with adequate sensitivity to detect the minimum protective level of tetanus antitoxin in the sera.