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

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.