HPV Genotyping of ThinPrep (Cytec) Cervical Cytology Samples with Weakly Positive Hybrid Capture 2 (Digene) Results
C Cleaves, K Hocker, L Sayage-Rabie, L Watson, M Taylor, S Nagori, V Pearson, A Rao. Scott & White Memorial Hospital, Texas A&M Health Sciences Center, Temple, TX
Background: Reflex testing for high risk (HR) human papillomavirus (HPV) on ThinPrep Pap (Cytyc) samples with diagnoses of ASCUS is the recommended standard. The Hybrid Capture 2 (HC2) assay (Digene) is currently the only FDA-approved method for this testing, although PCR-based research genotyping kits including the Linear Array (LA) HPV Test (Roche) are available. The significance of low positive (below 10 RLU) HC2 values is unknown, and Digene recommends repeat testing of values < 2 RLU. This study compares low positive HC2 values with genotyping results using the LA kit.
Design: 100 ThinPrep samples from 2007-2008 with HC2 results between 0.1 and 7.0 RLU were repeated and tested with the LA kit for both HR and low risk (LR) HPV types. All cytology slides were reviewed to re-evaluate the rendered diagnosis, and any additional follow-up cytology or histology was recorded if available.
Results: 49% of indeterminate (RLU 0.1-7.0) cases were positive for different HR genotypes, compared to 4.4% positives with repeat HC2. 21% of the cases were positive for HPV 16 and/or 18, but many other HR genotypes including 33, 39, 52, 56, 66, and 68 were identified. Of the samples indeterminate for HR HPV by HC2 that had only LR genotypes by LA, 21% contained HPV 53. This was twice the frequency of any other LR genotype.
Conclusions: ASCUS cases followed by positive HR HPV testing carry clinical implications, including referral for colposcopy. We believe that repeat testing of samples with low positive HC2 results has the potential for under-calling results and that screening with an alternate test such as the LA genotyping kit may be more sensitive. The high frequency of finding HPV 53 in cases of low positive HC2 HR HPV results may indicate a LR HPV type causing cross-reactivity in the HC2 assay.
Wednesday, March 11, 2009 9:30 AM
Poster Session V # 38, Wednesday Morning