Atypical squamous cells, cannot exclude a high-grade squamous intraepithelial lesion: the practice experience of a hospital-based reference laboratory with this new Bethesda system diagnostic category.

The 2001 Bethesda System diagnostic category of atypical squamous cells cannot exclude a high grade squamous intraepithelial lesion (ASC-H) was developed and implemented after many studies that proved its clinical relevance. In this study, we describe the practice experience of a hospital-based reference laboratory with this new diagnostic category. The anatomic pathology computer database was searched, and 414 Papanicolaou (Pap) smears signed out as ASC-H were discovered among 60,390 Pap smear accessions over a 17-month period of time. One hundred four cases had corresponding tissue specimens. Slides from all Pap smears and tissue specimens were reviewed, and five Pap smears were reclassified, leaving 99 study cases. In our laboratory, 88.9% of the study cases had either low or high grade dysplasia diagnosed on subsequent tissue specimens. The positive predictive value of ASC-H for histologically proven high-grade squamous intraepithelial lesions (HSIL's) was 40.4%. Of those having human papillomavirus (HPV) hybrid capture II testing, high-risk HPV types were detected in 73.9% of cases. The majority of study cases had less than 25 atypical cells. In two hysterectomy cases and three loop electrosurgical excession procedure (LEEP) conization cases, high-grade dysplasia was present as a single microscopic focus, suggesting that the paucity of atypical cells in ASC-H Pap smears may be secondary to small lesion sampling. Thirteen study patients were postmenopausal and 30.8% had low-grade dysplasia, and of these, 46.2% had high-grade dysplasia on subsequent tissue specimens. In conclusion, our practice experience with ASC-H is similar to that reported in the literature before the 2001 Bethesda System. Copyright 2005 Wiley-Liss, Inc.