Interlaboratory quality control in gynecologic cytopathology using the novel CONQUISTADOR software. Interobserver reproducibility in the Latin American screening study

OBJECTIVE: The recently developed software (CONQUISTADOR), capable of computing all intralaboratory and interlaboratory quality control (QC) indicators, was used to evaluate the diagnostic agreement among 4 cytology laboratories participating in the LAMS Study. STUDY DESIGN: The study was an interlaboratory exchange of specially designed 5 slide sets, each comprising 20 (conventional cytology) slides. At the first step, 80 slides (with "clear-cut" cases) were divided into four sets (A, B, C, D) of 20 specimens, each including inadequate and negative cases as well as in different proportions of all diagnostic TBS 2001 categories. In the second round, a fifth set (E) of 20 slides ("difficult cases") was designed, with all diagnostic categories, ASC and AGC included. Common measures of reproducibility (kappa and weighted kappa), accuracy (SE, SP, PPV, NPV) and 3 indices of diagnostic variability were calculated for sets A-D and set E, separately. RESULTS: For the 5 slide sets together, the weighted kappa was 0.8 (95% CI 0.76-0.85), which is the lower limit of the "almost perfect" ranking of kappa statistics, indicating an excellent interlaboratory agreement. The interlaboratory reproducibility was lower only for the difficult set (E). Similarly, the sensitivity for set E (70.0%) was lower than that (92.1%) for sets A-D. The diagnostic variability indices were not substantially different between the difficult (set E) and clearcut (sets A-D) cases. CONCLUSION: High interlaboratory reproducibility was obtained for sets A-D ("clear-cut" cases), while more interlaboratory variation was evident in the difficult samples. The new CONQUISTADOR software is a valuable tool in calculating the indicators needed in this intralaboratory and interlaboratory.