Prescreening of cervical smears using two-parameter flow cytometry. Cytologic identification of artifacts.

Individual properties of gynecologic specimens can produce artifacts in flow cytometric (FMC) measurements, possibly leading to false interpretations. An identification of such artifacts was undertaken by parallel FCM and microscopic investigations. One hundred fifty unselected cervical smears were measured by FCM using the fluorochromes 4'-6-diamidino-2-phenylindole (DAPI) for DNA and sulforhodamine (SR 101) for protein. Microscopic specimens were stained by the Papanicolaou technique, and a detailed cytogram was prepared from each smear. FCM discrimination of fluorochrome-stained superficial and intermediate cells was very difficult. On the other hand, a correlation could be established between the fraction of cells from the deeper epithelial layers in the microscopic cytogram and the mean protein content in the FCM histogram. Furthermore, the role of microorganism could be elucidated. Some microorganisms may produce a reduction of the protein content by cytolytic changes. Other microorganisms adhere to the cell surface, resulting in a misleading increase of the DNA fluorescence. Implications for the problem of false alarms are discussed.