The interpretation of ELISA results by means of the standard deviation ratio

An improved sensitivity to low levels of hepatitis B surface antigen (HBsAg) was demonstrated when ELISA results were interpreted by a statistical method. The absorbance of each test well was compared with the mean absorbance of all low-colour test samples. Those wells with an absorbance of more than two standard deviations above the mean were referred for confirmatory tests. Samples containing 1.0 ng/ml of HBsAg were reliably detected by a rapid assay technique (1.5 h). Predictive value analysis showed greater sensitivity than was possible from a direct comparison of test samples with controls.