APTIMA assay on SurePath liquid-based cervical samples compared to endocervical swab samples facilitated by a real time database

Abstract

Background: Liquid-based cytology (LBC) cervical samples are increasingly being used to test for pathogens, including: HPV, Chlamydia trachomatis (CT) and Neisseria gonorrhoeae (GC) using nucleic acid amplification tests. Several reports have shown the accuracy of such testing on ThinPrep (TP) LBC samples. Fewer studies have evaluated SurePath (SP) LBC samples, which utilize a different specimen preservative. This study was undertaken to assess the performance of the Aptima Combo 2 Assay (AC2) for CT and GC on SP versus endocervical swab samples in our laboratory. Materials and Methods: The live pathology database of Montefiore Medical Center was searched for patients with AC2 endocervical swab specimens and SP Paps taken the same day. SP samples from CT-and/or GC-positive endocervical swab patients and randomly selected negative patients were studied. In each case, 1.5 ml of the residual SP vial sample, which was in SP preservative and stored at room temperature, was transferred within seven days of collection to APTIMA specimen transfer tubes without any sample or patient identifiers. Blind testing with the AC2 assay was performed on the Tigris DTS System (Gen-probe, San Diego, CA). Finalized SP results were compared with the previously reported endocervical swab results for the entire group and separately for patients 25 years and younger and patients over 25 years. Results: SP specimens from 300 patients were tested. This included 181 swab CT-positive, 12 swab GC-positive, 7 CT and GC positive and 100 randomly selected swab CT and GC negative patients. Using the endocervical swab results as the patient’s infection status, AC2 assay of the SP samples showed: CT sensitivity 89.3%, CT specificity 100.0%; GC sensitivity and specificity 100.0%. CT sensitivity for patients 25 years or younger was 93.1%, versus 80.7% for patients over 25 years, a statistically significant difference (P = 0.02). Conclusions: Our results show that AC2 assay of 1.5 ml SP samples transferred to APTIMA specimen transfer medium within seven days is sufficiently sensitive and specific to be used to screen for CT and GC. CT sensitivity may be somewhat reduced in samples from patients over 25 years. SP specimens retained in the original SP fixative for longer time intervals also may have decreased sensitivity, due to deterioration of RNA, but this was not assessed in this study. The ability to tap the live pathology database is a valuable tool that can useful to conduct clinical studies without a costly prospective clinical trial.