title: Value of repeat testing using Cepheid GeneXpert CT/NG for indeterminate PCR results when diagnosing Chlamydia trachomatis and Neisseria gonorrhoeae.
abstract: Nucleic acid amplification tests (NAATs) are the most sensitive method for diagnosing chlamydia and gonorrhoea. We use the COBAS 4800 CT/NG combined assay (Roche Molecular Diagnostics, CA, USA), and whilst the majority of samples yield definitive results, a small proportion are reported as indeterminate. In these instances, it is usual practice to request repeat samples which delays diagnosis. This audit was twofold: first to establish the proportion of indeterminate results with current NAAT testing requiring re-sampling. Second, to determine whether a second NAAT such as Cepheid GeneXpert CT/NG assay (Cepheid, CA, USA) could be used on initial indeterminate samples to resolve indeterminate results, therefore reducing need for repeat sampling. During 2012, 144/21,931 (0.66%) samples were indeterminate for Neisseria gonorrhoeae, Chlamydia trachomatis or both, and a repeat sample was received in only 51.77% of patients with final results being delayed for more than 24 h. Over the next six months, there were 77/9472 (0.81%) indeterminate results. After an evaluation and introduction of the Cepheid assay, the number of indeterminate results fell to 9 (0.10%). Thus, use of the Cepheid assay significantly reduced indeterminate results, reduced reliance on a repeat sampling and significantly improved turnaround time, laboratory workflow and patient experience.
authors.affiliation: Department of Medical Microbiology, Ninewells Hospital and Medical School, NHS Tayside, Dundee, UK b.parcell@nhs.net.
authors.forename: Benjamin J
authors.initials: BJ
authors.lastname: Parcell
authors.affiliation: James Paget University Hospitals NHS Foundation Trust, Norfolk, UK.
authors.forename: Lasantha
authors.initials: L
authors.lastname: Ratnayake
authors.affiliation: Department of Medical Microbiology, Ninewells Hospital and Medical School, NHS Tayside, Dundee, UK.
authors.forename: Geraldine
authors.initials: G
authors.lastname: Kaminski
authors.affiliation: Department of Medical Microbiology, Ninewells Hospital and Medical School, NHS Tayside, Dundee, UK.
authors.forename: William J
authors.initials: WJ
authors.lastname: Olver
authors.affiliation: Department of Medical Microbiology, Ninewells Hospital and Medical School, NHS Tayside, Dundee, UK.
authors.forename: David L
authors.initials: DL
authors.lastname: Yirrell
mesh_terms: D001431:Bacteriological Techniques / Q000379:methods*; D002690:Chlamydia Infections / Q000175:diagnosis* / Q000382:microbiology; D002692:Chlamydia trachomatis / Q000235:genetics / Q000302:isolation & purification*; D005260:Female; D006069:Gonorrhea / Q000175:diagnosis* / Q000382:microbiology; D006801:Humans; D008297:Male; D025202:Molecular Diagnostic Techniques / Q000379:methods; D009344:Neisseria gonorrhoeae / Q000235:genetics / Q000302:isolation & purification*; D021141:Nucleic Acid Amplification Techniques; D016133:Polymerase Chain Reaction / Q000379:methods*; D011237:Predictive Value of Tests; D012680:Sensitivity and Specificity
keywords: Cepheid GeneXpert CT/NG; Chlamydia trachomatis; Neisseria gonorrhoeae; Sexually transmitted infection; confirmation; diagnosis; indeterminate results; nucleic acid amplification test