Abstract
A modified counterelectrophoresis (CEP) method was developed for determining the d and y subtypes of hepatitis B antigen (HBSAg). In this method, HBSAg of known subtype was diffused into the agarose gel before electrophoresis from the wells which were subsequently to receive the subtyping antiserum. This served to absorb the common anti-alpha antibody from the subtyping antiserum, which was heterologous with respect to the d or y component, during electrophoresis. The remaining d or y antibody then reacted type specifically with the antigen to be subtyped. The modified CEP method was much more sensitive than the immunodiffusion (ID) method for subtyping HBSAg. Sixty-two sera which could not be subtyped by ID were successfully subtyped by the CEP method. The geometric mean HBSAg complement fixation titer determined on 48 of these sera was significantly lower (P congruent to 0.016) than that of a group of sera which could be subtyped by ID. Sixteen other sera could not be subtyped by either the CEP or the ID procedure (geometric mean titer equal to 5.2). Therefore, more sensitive means of subtyping must be used for some HBSAg-positive sera.