Introduction of the Thin Prep Imaging System (TIS): experience in a high volume academic practice

Since the introduction of the liquid-based ThinPrep testing in 1996, most cytology laboratories across the country have adopted the liquid-based cytology (LBC) for Pap test screening. Subsequent to wide-spread adoption of the ThinPrep Pap test, the ThinPrep Imaging System (TIS) Cytyc Corp, Marlborough, MA was introduced to improve the accuracy and efficiency of screening interpretation. We report our initial experience with the TIS at Magee Women's Hospital. We introduced the TIS in December 2004.

The imager assisted Pap test results over the first 12 months (December 2004 to December 2005) of implementation were reviewed and analyzed. Our implementation protocol included each cytotechnologist manually prescreening 200 negative slides to gain experience with the imager slides and serve as a quality check for the TIS. We re-screened 3400 slides (200 slides each for 17 cytotechnologists) manually which were initially determined to be negative using the TIS. 104,457 Pap tests were imaged on the TIS. 95,899 manually screened Pap tests, 12 months prior to the introduction of the TIS (December 2003-November 2004) are taken as the historic control group for our study.

The mean ASC-US rate employing the automated imager was 8.70% [9088/104,457]. The mean LSIL detection rate was 4.22% [4409/104,457]. The imager did not miss any detectable high-grade lesions during these months, with a HSIL (+) detection rate of 0.68% in comparison to 0.60% by manual screening confirmed by follow-up biopsies. The difference is statistically significant with a p value of 0.022. The definition of false negative rate for purposes of this study is calculated as the number of false negative cases identified out of number of negatives re-screened. The TIS false negative rate was estimated at 0.012% [4/3400].

The overall performance of the TIS in our lab appears to be highly satisfactory in terms of improving sensitivity in screening cervical precursor lesions. The increased accuracy of detection of HSIL indicates a positive impact of the TIS in our laboratory.