Respiratory cytodiagnosis: study in observer variation and its relation to quality of material.

Sensitivity and accuracy of cytodiagnosis were assessed in a multicentre study. Six centres each provided sputum cytological material from 20 cases. Each centre screened and reported on the 100 slides provided by the other five centres. The reports were assessed against consensus reference diagnoses, reached by discussion with transparencies, histological sections, and closed-circuit television. False positive rates of 0-4% (average 1.3%) and false negative rates of 0-12% (average 5.0%) of slides examined were recorded. The order of agreement on the three common cell types was adenocarcinoma 75% (50-91%), squamous cell carcinoma 80% (59-94%) and small carcinoma 95% (71-100%). The effect of quality of material on cytological opinion was assessed by comparing disagreement rates on each of the different sets of 20 slides. Disagreement varied from 1% to 23% depending on which set of material was examined.