Are significant numbers of abnormal cells lost on the discarded ThinPrep® broom when used for cervical cytology?

Abstract

Are significant numbers of abnormal cells lost on the discarded ThinPrep® broom when used for cervical cytology? In view of a study with SurePath® showing that cells were lost on the broom if it was discarded, we decided to investigate whether cells were lost on the ThinPrep® (TP) broom, which is discarded according to the manufacturer's protocol. To determine whether significant amounts of cellular material are lost on the discarded TP broom, and whether the loss is operator dependent. Three hundred and six women attending the Guy's Hospital Colposcopy Unit gave their consent for TP liquid-based cytology samples to be taken and the broom immersed in a second vial instead of being discarded. The cellularity of the first and second vials was compared by counting cells in 10 ×40 high-power fields (HPFs). The significance of cell loss was ascertained by correlating the likelihood of abnormal cells and transformation zone (TZ) material being present with the degree of cellularity of the two vials. More than 10 cells per HPF were seen in 3.2%, 19.4% and 35.8% of slides from the second vial taken by three experienced colposcopists, which was significantly different between them (P < 0.001); cellularity of the first vial was not significantly different between colposcopists but the one with highest cellularity in the first vial discarded most in the second. Abnormal cells were more likely to be seen in slides with more than 10 cells per HPF (P < 0.001) and with evidence of TZ sampling (P < 0.001), but there was no preferential loss of TZ material in the second vial. Of 126 slides with abnormal cells on the slides from the second vial, 113 (89.7%) were also present on the significantly more cellular first vial (P < 0.001). Abnormal cells were potentially lost on the broom, but were usually represented in the first vial. The likelihood of abnormal cells being discarded was operator dependent in this small study, but this did not affect the quality of the initial preparation. The likelihood of abnormal cells being seen on TP slides was dependent on their cellularity, which provided our laboratory with a criterion for the assessment of sample adequacy.