An indirect haemagglutination test for demonstration of gonococcal antibodies using gonococcal pili as antigen. II. Serological investigation of patients attending a dermato-venereological outpatients clinic in Copenhagen.

A total of 1223 serum specimens were obtained from 649 consecutive patients attending a dermatovenereological out-patient clinic in Copenhagen with a request for venereal disease control. The sera were examined for gonococcal antibodies by both a gonococcal complement fixation test (GCF) and an indirect haemagglutination test using gonococcal pili as antigens (IHA). The diagnosis of current gonococcal infection in 28 per cent of the patients was based on positive culture for Neisseria gonorrhoeae from one or more of the following sites: urethra, rectum and fauces in all patients, and/or cervix in female patients. The specificity, sensitivity and predictive values of positive and negative test results were calculated for the various groups of patients on the assumption that all positive results, both in patients without gonorrhoea but with a previous gonococcal infection and in patients without known current or previous infection, were false positives. The following values were found: Sensitivity: IHA 45-100%, GCF 6-29%. Specificity: IHA 65-89%, GCF 97-100%. Predictive value of positive test result: IHA 43-74%, GCF 69-100%. Predictive value of negative test result: IHA 78-100%, GCF 61-85%.