False-positive gonorrhea test results with a nucleic acid amplification test: The impact of low prevalence on positive predictive value

Five false-positive gonorrhea test results from a private laboratory using a nucleic acid amplification test led to an investigation by the Hawaii State Department of Health. No unexplained increase or variation in the laboratory's positive gonorrhea test results was detected. The proportion of positive gonorrhea test results among tests performed in the population was 1.06%. The calculated positive predictive value (PPV) of the test in this setting was 60%. Documentation of sexual histories was lacking for all cases. It is imperative to obtain a sexual history for both assessing sexually transmitted disease ( STD) risk and interpreting STD test results. The possibility that positive test results may be false should be considered when patients have unanticipated positive test results. Clinicians who perform STD screening tests should know the approximate prevalence of STDs in the population being screened and have a conceptual understanding of PPV and the impact of low prevalence on screening tests with imperfect specificity.