A modified reversed passive hemagglutination test for the detection of hepatitis B
surface antigen HBsAg is described. Sera and reagent cells coated with antibody to HBsAg
(anti-HBs) are loaded separately into the rotor of a miniature centrifugal fast analyzer. The
rotor is centrifuged briefly to transfer the components into its cuvettes. After mixing, the
suspensions are allowed to stand at room temperature for 30 min, following which the rotor
is again centrifuged and the absorbance of each cuvette is monitored. Cells suspended in
serum containing HBsAg leave the light path more rapidly than cells suspended in sera free
of antigen. The magnitude of change in absorbance varies directly with the concentration of
the antigen.
In 45 sera tested by the conventional V-plate technique, findings were as follows: 21 positive,
19 false positive and 5 negative. The automated procedure unequivocally differentiated the
21 positives; results for the false positive and negative specimens were identical and clearly
distinguishable from the positive results. The automated procedure enhances specificity, offers
equivalent sensitivity, and results that are quantitative and objective.