United Kingdom scheme for external quality assessment in virology. Part II. Specimen distribution, performance assessment, and analyses of participants' methods in detection of rubella antibody, hepatitis B markers, general virus serology, virus identification, and electron microscopy

Abstract

Methods for the preparation and pre-distribution testing of specimens for external quality assessment in virology have been defined and criteria for allocation of scores for participants' reports on each category of specimen have been established. Specimens for detection of rubella antibody or markers of hepatitis B infection consist of human serum samples, which are distributed after detailed assessment of the expected results. In testing for rubella antibody or hepatitis B surface antigen (HBsAg) the scores given for reports of positive, equivocal, or negative depend on the specimen's content of antibody or HBsAg as established in the external quality assessment laboratory. For general virus serology two serum samples must be tested against a designated antigen by the complement fixation method; the score allocated for each participant's results depends on the ratio of the two titres he records, which is then compared with a target value derived from the results of a panel of participating laboratories. In virus identification and electron microscopy specimens are prepared from cultures or from clinical samples, and scores depend on the accuracy of identification. The pre-distribution tests necessary to establish the virus content and stability of these specimens have been defined, and media suitable for transporting specimens for virus culture, fluorescent antibody staining, or electron microscopy have been developed. A participant's overall success rate for each specimen is judged from the mean score (maximum 2) calculated from the scores of all participants examining the specimen. Mean scores were highest for detection of rubella antibody or HBsAg (from 1.67 to 1.96) and lowest for specimens containing certain small enteric viruses distributed for electron microscopy (0.82 to 1.12). Participants' reports on the methods used for each specimen have been analysed. Current changes and developments in methods have been recorded, and attempts have been made to relate the use of various techniques and test kits to successes or failures with various types of specimen.