Thin-layer Pap test vs. conventional Pap smear. Analysis of 400 split samples

Abstract

Objective: To analyze our experience with 400 Thin-Prep (TP) split samples (Cytyc Corp., Boxborough, Massachusetts) as an initial assessment of this new technology's effect in our laboratory.

Study design: Three gynecologic oncologists and two general gynecologists obtained the 400 split samples using a broom sampling device. Following conventional smear (CS) preparation, they rinsed the broom in Preservcyt solution (Cytyc) for subsequent TP processing. The paired samples were separated, independently analyzed and classified by the Bethesda System. All available follow-up surgical pathology material was reviewed and compared to the cytologic diagnoses.

Results: TP had significantly more abnormal results (22% vs. 16%, P = .007), including more atypical squamous cells of undetermined significance (ASCUS) (9.5% vs. 6.3% P = .07) and low grade squamous intraepithelial lesion (LSIL) (7.8% vs. 5.3%, P = .03). Both methods had 3.3% high grade squamous intraepithelial lesion (HSIL). For TP, ASCUS/squamous intraepithelial lesion (SIL) = 0.86 and for CS, ASCUS/SIL = 0.74. Ten TP SILs had a paired negative CS, including LSIL (nine cases) and HSIL (one case). Consensus review of these 10 TP slides confirmed the HSIL and four LSILs. No CS SILs had a paired negative TP. Only 36 (9%) cases had surgical pathology follow-up. The surgical specimens included 17 cervical intraepithelial neoplasia (CIN) 2 or above. The TP method had no false negatives, while the CS method had 3 false negatives among the 17 confirmed cases of CIN 2 or above.

Conclusion: TP appears to be superior to CS for detecting SILs.