A new immunonephelometric method is described for the quantification of antibodies against factor VIII in sera from patients suffering from haemophilia A. We have been able to reduce the reaction time to only 16 minutes, which permits its application to emergency cases. Applying Spearman's test, we have correlated the results obtained by the immunonephelometric and Ruggieri's methods, obtaining r = 0·87, p<0·01 for n = 11. From the reproducibility studies we obtained SD = 1·16 as maximum dispersion value. Because it is a fully automated method in a continuous-flow system, the possible manual errors are reduced to a minimum; 60 determinations can be carried out in 1 hour.
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