A collaborative trial of a semi-automatic system for slide preparation and screening in cervical cytopathology

We report a test of an experimental system for machine-aided screening in cervical cytology, comprising the 'CYTOPRESS' semi-automatic slide preparation system (Nijmegen) and the 'CERVIFIP' interactive scanner (Edinburgh). Material from women attending clinics in Edinburgh and Nijmegen was stratified according to the severity of the conventional laboratory diagnosis and selected randomly within strata for inclusion in the test. Monolayered slides were prepared by CYTOPRESS from cervical scrape material remaining after preparation of conventional smears and scanned by CERVIFIP to determine the positions of the most 'suspicious' objects. The test was based on a set of 701 monolayers, divided equally between 'negatives' and 'abnormals' of various grades, of which 585 (83.4%) were passed automatically as adequate for machine-aided analysis. Approximately 15% of adequate slides were passed as 'negative' without operator interaction. In the remaining 85%, the suspicious objects were inspected by a human operator and a decision was then made either to refer each monolayer for conventional microscopic analysis, or to pass it as 'negative'. Where discrepancies occurred between the conventional laboratory and the system results, a consensus diagnosis was reached by taking into account all relevant information including clinical data. Of those with a consensus diagnosis of CIN 3 or worse an estimated 9.3 +/- 4.1% were passed by the system as 'negative'. Closer investigation of these false-negatives revealed that most, and perhaps all, were preventable by system improvements either planned or in progress. Corresponding false-negative rates for those graded 'CIN 1 or 2' and 'negative-early recall' were estimated, respectively as 18.9 +/- 5.3% and 22.9 +/- 3.1%. Of those with a 'negative-routine recall' consensus, 19.4 +/- 2.5% were referred for conventional microscopic analysis, a level well within acceptable limits for cost-effectiveness. Women whose initial laboratory smears were negative, but whose consensus diagnosis was 'negative-early recall' or CIN, are being investigated further to determine whether cervical abnormalities were in fact present. Over two-thirds of this group were referred by the machine-aided system for conventional microscopic analysis.