Split-sample analysis of discarded cells from liquid-based pap smear sampling devices

Objective: To examine cells that were retained on sampling devices used to collect ThinPrep™ (Cytyc Corp., Boxborough, Massachusetts, U.S.A) Pap smears in order to evaluate both the number and significance of cells that are routinely discarded with these devices after liquid-based specimens are collected. Study Design: One hundred Pap smears from 100 women were prospectively procured after gynecologic Pap smears were collected for the ThinPrep™ Pap test. The sampling end of the collection devices was cut off and placed in a vial that contained SUREPATH™ preservative fluid (TriPath Imaging, Inc., Burlington, North Carolina, U.S.A.). The residual cell samples were processed using the SurePath™ PREPSTAIN™ slide processor (TriPath). A single liquid-based slide was prepared from the sampling devices from each of the 100 specimens collected. The slides produced from the discarded devices were reviewed for the following: squamous cells, endocervical component, epithelial cell abnormalities and miscellaneous findings. The slides prepared from the "throw-away" (TA) material were subsequently compared with the primary ThinPrep™ Pap smear slide. Results: Twenty-five percent of the TA samples had an equal or greater number of squamous cells per high-power microscopic field when compared to the primary ThinPrep™ slide, with 8% of the TA slides demonstrating greater overall cellularity. An endocervical component was present on 27 of 66 cervical samples (40.9%). Three of five cases (60%) interpreted as atypical squamous cells of undetermined significance had similar cells on the TA slides. Two cases of atypical glandular cells of undetermined significance had no abnormal cells on the TA slides. Twelve of 14 cases (85.71%) of low grade squamous intraepithelial lesion contained similar cells on the TA slides. Two of four cases (50%) of high grade squamous intraepithelial lesion also had similar abnormal cells on the TA slides. Miscellaneous findings included 1 case of benign endometrial cells and 4 Candida infections present on both preparations, along with 1 case of Trichomonas vaginalis organisms present on the ThinPrep™ slide only. In 1 specimen, several multinucleated histiocytic giant cells were present only on the TA slide. Conclusion: Specimens prepared from TA collecting devices used for the ThinPrep™ Pap test are less sensitive than the primary specimen for the detection of cervical lesions. This is in contrast to split-sample studies involving ThinPrep™ and conventional smears. Our study documented the presence of normal and abnormal cells discarded from ThinPrep™ sampling devices in a high percentage of cases. Discarded abnormal cells on the TA slides were, however, few when compared to the primary specimen, with only 1 exception involving a high grade lesion.