[False negative Pap smears in a Danish material]

The aims of screening against cervical cancer are: 1) to reduce the number of cervical cancer cases, 2) to diagnose the cervical carcinoma precursor lesions of which treatment is quite simple and 3) to use the available resources in the best possible way. The purposes of this study were firstly to get an impression of the false negative rate in the County of Funen, secondly to illustrate some of the causes, and thirdly to recommend some ways to reduce the false negative cases in the future.

All previously negative Pap smears in the period from April 1, 1989 to December 31, 1999 from women who had shown at least moderate dysplasia histologically in the period from Jan 1, 1996 to December 31, 2000 were reevaluated.

A total of 551 Pap smears were rescreened. Eighty-one per cent were sampling errors and the rest was regarded as interpretation and screening errors. The false negative rate for a single year, 1991, was assessed at 22%. The false negative rate of interpretation and screening errors was 4.6%.

The results are in accordance with other studies. We describe three characteristical cytological cell patterns as the main causes of the false negative samples. To prevent false negative samples a very important factor is thorough training and further education of the staff. Furthermore, a change into liquid-based cytology will raise the quality both of the cell sample and of the screening procedure.