Quality control (QC) of Papanicolaou (Pap) smear testing focuses on the identification of screening errors by 10% random, rapid, or thorough manual rescreening of some portion of negative smears. One hundred percent thorough manual rescreening has been reported to be the most effective method of identifying screening errors in conventional Pap smears (CP), but to the authors' knowledge no experience with this QC method has been reported for the ThinPrep Pap test (TP). The current study reports the estimated screening error rate of TP as determined by a QC program using 100% thorough rescreening.
All TP samples received at the study institution between January 1, 1999 and December 31, 2000 and initially screened as negative underwent thorough manual QC rescreening.
A total of 53,419 TP samples were received during the study period. Of these, 5,368 cases (10%) initially were interpreted as abnormal. A total of 47,247 cases (88.4%) were rescreened. Abnormalities were identified in 804 additional cases, for a screening error rate of 13.0%. Of the 804 cases, 678 (84.3%) were atypical squamous cells of undetermined significance, 116 (14.4%) were low-grade squamous intraepithelial lesions, and 10 (1.2%) were high-grade squamous intraepithelial lesions. No tumors were identified on rescreening.
In the current study, 100% thorough rescreening of TP samples was found to result in the detection of a significant number of abnormalities that would have been missed by routine random 10% QC rescreening. The screening error rate determined by 100% thorough QC rescreening of TP is comparable to that reported for CP QC rescreening.