Kinetic latex agglutinometry II: a rapid, quantitative assay for factor VIII antigen.

A rapid method for measuring factor VIII antigen in plasma is presented, based upon optical measurement of the rate of agglutination of a stirred suspension of latex particles coated with anti-factor VIII immunoglobulin, when mixed with plasma containing factor VIII antigen. A log-log relationship exists between factor VIII concentration and the reciprocal of the time required for a fixed absorbance change. The assay is rapid, requiring less than 3 min for normal plasma, involves stable reagents, and can be performed with conventional instrumentation. Antigen values in normal plasma a well as plasma from patients with von Willebrand's disease (angiohemophilia) correlate well with values measured by electroimmunoassay or by radioimmunoassay.