A solid-phase enzyme-linked immunosorbent assay (ELISA), based on the "sandwich" principle with use of microtiter plates, was developed for the detection of hepatitis B surface antigen (HBSAg). Results could be read within one day by the naked eye or by colorimeter. The detection level was less than or equal to 5-10 ng of HBSAg/ml. The sensitivities of ELISA and radioimmunoassay were about the same in dilution series and in a follow-up study of 19 patients with acute hepatitis B infection. In 11 European medical centers where greater than 50,000 samples were tested, ELISA detected significantly more HBSAg-positive samples than a reversed hemagglutinatiom test. No significant difference in sensitivity between ELISA and radioimmunoassay could be demonstrated. On the average, 2.2% of readings were false-positive reactions. Falsely positive samples were identified by a confirmatory test.
