Information, discrimination and divergence in cytology. IV. Quality control in diagnostic cytology.

The performance of diagnostic cytology on Papanicolaou smears can be periodically monitored by calculating the total discrimination or the total divergence of the cytologic diagnoses against the histologic diagnoses on samples obtained by colposcope-directed biopsies. Using these measures, the annual performances of the Gynecologic Cytology Laboratory of the University of Minnesota between 1980 and 1988 were retrospectively analyzed. For those years, the total discrimination and total divergence behaved similarly and were sensitive to the performance of the total system, including specimen sampling errors and laboratory precision. The lowest limits of the permissible range of the total discrimination and total divergence were 0.15 and -1.21 decits, respectively, for a single-slide Papanicolaou test if an 80% "hit" rate was accepted as the lowest threshold for each category. The optimal numbers of category-states were not a sensitive indicator of the quality of a laboratory; i.e., the optimal number of diagnostic categories remained at three throughout the period studied.