False negatives in focused rescreening of Papanicolaou smears: how frequently are 'abnormal' cells detected in retrospective review of smears preceding cancer or high-grade intraepithelial neoplasia?

Abstract

The 5-year retrospective rescreening process is an integral part of the cytology laboratory's quality assurance program. Its major role is the identification of errors in screening and/or interpretation that represent rare events and patterns. Recognition of such errors can provide for reorientation and reeducation of cytology personnel, ultimately to improve prospective accuracy. Careful research studies have shown that retrospective rescreening may identify abnormalities on slides diagnosed as negative in more than 50% of cases analyzed. Surveys of actual clinical laboratory programs show detection of abnormalities in significantly lower percentages, generally in the range of 10% to 30%. The majority of cases identified are reclassified in the category of atypical squamous cells of undetermined significance. Cases of identified high-grade squamous intraepithelial lesion are identified as a minority of cases in virtually all laboratories surveyed. In the cases reassessed as high-grade squamous intraepithelial lesion, a common cytologic pattern is that of a few isolated, small, "immature metaplastic," dysplastic cells being present.