The 2001 Bethesda system sought to eliminate the confusion around an ASC-US diagnosis, by better defining criteria, encouraging downgrading to negative for intraepithelial lesion and malignancy (NILM) when possible, and introducing a new atypical category--atypical squamous cells of a high-grade squamous intraepithelial lesion cannot be ruled out (ASC-H).
The 1988 Bethesda terminology was used for each study, except for the Nygard et al (12) study, which used a system that had greater similarity to 2001 Bethesda, which included an ASC-H category.
This category includes those cases with classic features of LSIL along with cells suspicious for a high-grade lesion (ASC-H) in a single sample.
Kaiser clinicians also crossed the HPV guidelines to test for HPV in 161 women with Pap results showing "atypical squamous cells, cannot exclude high-grade squamous intraepithelial lesions" (ASC-H).
Among 125 of the women with ASC-H who also had biopsies, 38% had CIN2/3+, including one adenocarcinoma in situ.
Fetterman described how the high negative predictive value of the HPV test for CIN 2/3+ and the falling HPV positivity rate with age make it useful to triage women with ASC-H. HPV triage of women with ASC-H would send 64% of women of all ages and 48% of women aged 30 and over to colposcopy.