Quality and liability issues with the Papanicolaou smear: the problem of definition of errors and false-negative smears.

A universally accepted definition for a false-negative Papanicolaou smear has not been established. Therefore, it is important to specify the criteria used to define false-negative smears when discussing the performance of clinical cytology. If these variables are not specified, there is potential for miscommunication. Variables include sampling versus laboratory false-negative errors, the definitions of what constitutes disease and the threshold to define an error, the time interval to detection, and the mechanism for detection of errors. False-negative error rate is defined as the number of false-negative Papanicolaou smears divided by the number of patients with disease. Discrepancy rate is often used interchangeably with false-negative rate, but the former does not factor in the prevalence of disease and the threshold used to define an error. The false-negative fraction is most useful for interlaboratory comparison. A reasonable definition of a laboratory false negative is a smear originally reported as negative or normal that is found to have sufficient numbers of carcinoma or dysplastic cells on review. The abnormal cells should be verifiable by more than one experienced cytologist in a blinded fashion, and it is ideal if the lesion is confirmed by biopsy or other confirmatory test.