False positive cervical smears: a cytometric and histological study.

The evidence of exfoliative cytology of the cervix uteri depends on various factors. The rate of false positive cervical smears is on average 8.8%. We have reviewed 170 false positive routinely Papanicolaou-stained cervical smears and the corresponding histological specimens. The aim was to look for non-neoplasic changes explaining the cytological over-interpretation. In addition, nuclear Feulgen-DNA measurements of the smears were made to look for changes in DNA pattern. In 50% of all cases, a cause was found for the false positive cytological diagnosis by means of histological reexamination: non-neoplastic nuclear and cellular polymorphia, severe purulent-erosive inflammation, a higher reclassification or a positive presurgical biopsy. In 51.9% of these cases, there were signs of an infection with human papilloma virus (HPV). In cases without histological explanation of the cytological findings, DNA measurements were made on the suspicious cells. By means of single cell algorithm (5c/9c exceeding events), a general rate of 62.7% of aneuploid specimens was detected. The number of aneuploid single cells ranged between 5 and 63 per slide. Of these cases, 23.1% showed signs of HPV infection. As a result of the study, the number of real 'false positive' cytological diagnoses decreased from 170 to 97 as a result of histological reexamination and DNA measurement. In doubtful cases, DNA measurement of suspicious smears should be made.