C-154. Confirming Positive GEN-PROBER APTIMAR TIGRISR DTSR COMBOR Neisseria gonorrhoeae and Chlamydia trachomatis Results: APTIMA CT and APTIMA GC Single Analyte Assays vs. Repeat testing on COMBO 2

M. T. Katanik, M. Sikorski, K. Marigney, S. Schindler, C. Starkey, G. S. Hall;
Cleveland Clin., Cleveland, OH.

Background: The APTIMA TIGRIS DTS COMBO 2 (COMBO) (Gen-Probe Inc. San Diego, CA) detects Neisseria gonorrhoeae (GC) and Chlamydia trachomatis (CT) nucleic acid using Target Capture, Transcription-Mediated Amplification and Hybridization Protection Assay. False positives have not been reported, however, confirmation or repeat testing is recommended if the prevalence of the organism is low in population being tested. The APTIMA CT (A-CT) and APTIMA GC (A-GC) assays are single analyte assays which differ from the COMBO assay in the specific region of rRNA used for replication and detection. This is the preferred method for confirmation. Repeat testing using COMBO is also an accepted means of assuring that a positive is a true positive. Methods: 124 patients positive (+) for CT and 75 patients + for GC using the COMBO were retested with the A-CT and A-GC assays. Another set of specimens with 178 + CTs, 41 + GCs and 29 multiple + (CT and GC +) were repeated on COMBO assay. All testing was done per manufacturer’s guidelines. Results: 122 /124 (98%) CT + specimens and 75/75 (100%) GC + specimens by COMBO were confirmed using the A-CT assay or A-GC assay respectively. The 2 discrepant CT results had relative light unit (RLU) values in the low + range on the initial COMBO run. When + results for another 178 specimens on the COMBO were repeated on COMBO, 176/178 (99%) CT + specimens, 41/41 (100%) GC + specimens and 29/29 (100%) CT+/GC+ specimens repeated as positive. One discrepant CT, initially CT +/GC- repeated twice as CT-/GC+. The other discrepant CT initially had a low + RLU value which repeated as negative. Conclusions: We were able to demonstrate a very low level of false + results for both CT and GC with either repeat testing of initially + results with COMBO assay or confirmation using the A-CT and A-GC confirmation assays. Utilizing the confirmation kits requires additional run time separate from routine patient runs and does require the purchase of these separate assays. Repeat testing on COMBO, which can be included in the routine patient runs, is cost and time efficient, while providing the same level of assurance that initially positive results are accurate.