HBsAg in urine: a new approach for the detection of urinary antigens

In order to define the optimal conditions for detection of microbial antigens in urine, urinary HBsAg excreted during hepatitis B was chosen as a model. Using commercial kits, which mainly involve anti-discontinuous epitopes, we found urinary HBsAg in only 50% of patients with HBsAg in their sera. In contrast, with an inhibition method involving a monoclonal antibody recognizing a continuous epitope, urinary HBsAg was found in 100% of these patients. Structural analysis of HBsAg showed that urinary HBsAg is denatured; it can escape detection by commercial kits well fitted for detection of native serum HBsAg. General implications for the revelation of urinary microbial antigens are discussed.