Comparative analysis of conventional Papanicolaou tests and a fluid-based thin-layer method

Abstract

Context: A fluid-based, direct-to-vial method of thin-layer gynecologic cytology (ThinPrep Pap Test) is reported to be more effective than the conventional Papanicolaou test in the detection of squamous intraepithelial lesions.

Objective: This retrospective analysis evaluated the validity of the findings on the thin-layer method using case material at a large independent laboratory and represented a comparison of performance of both methods over an identical period.

Methods: Data for conventional and ThinPrep tests were compared for 2 periods. Period 1 included 1,421,080 conventional and 56,835 ThinPrep specimens, and period 2 included 564,270 conventional and 109,784 ThinPrep specimens. Squamous intraepithelial lesions were used to determine detection of disease. These 2 sets of data were also analyzed to eliminate effects of any selection bias toward ThinPrep for high-risk patients.

Results: Use of ThinPrep showed a greater than 100% increase in the detection rate of squamous intraepithelial lesions (1.3%-3.4% in period 1 and 1.3%-2.9% in period 2), which was statistically significant after correcting for selection bias. We also found a significant decrease in the false-negative proportion (57% in period 1 and 35% in period 2). There was a marked improvement (233%) in the detection of high-grade squamous intraepithelial lesions in high-risk cases and a decrease in the atypical squamous cells of undetermined significance to squamous intraepithelial lesion ratio from 3.1 to 1.5 in period 2.

Conclusion: ThinPrep is better than the conventional Papanicolaou test in detecting squamous intraepithelial lesions and is a superior screening test in detection of precancerous changes of the cervix.