PubMed · 6113468
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J A Lunn. 1981-07-11. Tuberculin testing.. https://doi.org/10.1016/s0140-6736(81)90445-1
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BACKGROUND: Although the false-negative rate (FNR) is the most important quality control measure for Papanicolaou smear screening, accurate, precise, and feasible methods for determining this value are lacking. METHODS: The author undertook an analysis and review of the literature. RESULTS: The best estimates of the FNR using atypical squamous cells of undetermined significance (ASCUS) as a threshold range from 17% to 61%. Sources of error in the accuracy of this measure that must be accounted for include the FNR of the review method, differences in diagnostic thresholds between the original diagnostic method and the review method, and differences in diagnostic accuracy between the original diagnostic method and the review method. Statistically precise (valid to within 10%) measurement of this value in laboratories with an ASCUS+ rate of 7% can be made from interlaboratory rescreening of approximately 1200-1500 randomly selected normal and abnormal slides along with both laboratories rediagnosing without rescreening 300-400 benign cellular change and ASCUS slides to determine the difference in diagnostic threshold. Consensus for each slide is not required with this method. Changing the threshold to low grade squamous intraepithelial lesion (best estimate FNR, 14-58%) requires review of significantly more slides to achieve the same statistical level of precision. CONCLUSIONS: Detailed analysis of the sources of error in determining the FNR allow creation of methods that are relatively unbiased, feasible, and testable and whose accuracy and precision can be determined.
BACKGROUND: Routine quality control rescreening often is used to calculate the false-negative rate (FNR) of gynecologic cytology. Theoretic analysis suggests that this is not appropriate, due to the high FNR of rescreening and the inability to actually measure it. The authors sought to determine the FNR of manual rescreening in a large, prospective, two-arm clinical trial using an analytic instrument in the evaluation. METHODS: The results of the Autopap System Clinical Trial, encompassing 25,124 analyzed slides, were reviewed. The false-negative and false-positive rates at various thresholds were determined for routine primary screening, routine rescreening, Autopap primary screening, and Autopap rescreening by using a simple, standard methodology. RESULTS: The FNR of routine manual rescreening at the level of atypical squamous cells of undetermined significance (ASCUS) was 73%, more than 3 times the FNR of primary screening; 11 cases were detected. The FNR of Autopap rescreening was 34%; 80 cases were detected. Routine manual rescreening decreased the laboratory FNR by less than 1%; Autopap rescreening reduced the overall laboratory FNR by 5.7%. At the same time, the false-positive rate for Autopap screening was significantly less than that of routine manual screening at the ASCUS level (4.7% vs. 5.6%; P < 0.0001). Rescreening with the Autopap system remained more sensitive than manual rescreening at the low grade squamous intraepithelial lesions threshold (FNR of 58.8% vs. 100%, respectively), although the number of cases rescreened was low. CONCLUSIONS: Routine manual rescreening cannot be used to calculate the FNR of primary screening. Routine rescreening is an extremely ineffective method to detect error and thereby decrease a laboratory's FNR. The Autopap system is a much more effective way of detecting errors within a laboratory and reduces the laboratory's FNR by greater than 25%.