The false negative smear. II. The trapping effect of collecting instruments.

One hundred and sixty-six conventional instruments of cell sampling used in gynecologic cytology were investigated after collecting tumor cells and normal squamous cells in vitro. Histologic preparations as well as scanning electronmicroscopic observations of wooden spatulas and cotton swab applicators revealed that despite smearing the material onto a slide, a large number of tumor cells remained trapped in the frames of such instruments. Five percent of the smears obtained showed no tumor cells. Similar results were obtained in preliminary observations in gynecologic patients having cervical atypias. The possibility was entertained that wooden spatulas and cotton swabs may be a source of some of the false negative results in gynecologic cytology.