The Efficacy of Liquid-Based Cervical Cytology Using Direct-to-Vial Sample Collection

Limitations

Our study is subject to several limitations. Most important, the observed differences in Pap test performance may have been because of actual differences of cervical neoplasia prevalences between the 2 groups, rather than a difference between Pap tests. Our subjects were selected from comparable patient populations by a study design that other researchers^10,11,16-20 have used to evaluate the direct-to-vial technique. Other than sampling a population of women with LBCC and then having them return for a CPT 1 month later, which risks compliance failure and spectrum of cervical disease changes or acquisition of new disease, there is no other study design to evaluate a direct-to-vial technique. One may question whether our increased rate of neoplasia detection demonstrated by LBCC is due to a substantial number of LBCC false-positive results.²¹ Yet, because the positive predictive values for the LBCC and CPT were similar and there were 3 times as many women with biopsy results of CIN 1 or greater in the LBCC group compared with the CPT group when only women with LSIL or greater Pap test results were considered, the increased rates of SIL detection using LBCC appear to represent an increased detection of true disease and not false-positive results, further validating our findings.²¹ The equivalent results for LBCC and CPT specificity (99%) indicate that the increased rate of SIL detection by LBCC was not due to a reduced specificity. Also, the favorable test results demonstrated for LBCC are not entirely dissimilar from those of other studies that used a split sample technique, a more biased study design for LBCC.^6-9 Studies by Vassilakos and colleagues¹⁶ and Papillo and coworkers¹⁰ demonstrated that a liquid-based thin layer cytologic report of LSIL or more severe disease correlated better with histologic results of CIN 1 or greater (80.5% and 80.2%, respectively) than CPTs (71.7% and 72.2%, respectively). Finally, because of the limited number of women with cervical caner in this study population, we were unable to determine if there were any differences between LBCC and the CPT in their ability to detect cervical cancer.

Conclusions

Compared with the CPT, LBCC detected a significantly greater percentage of satisfactory Pap tests and significantly reduced the number of unsatisfactory and SBLB tests. These findings demonstrate that LBCC significantly improves the adequacy of Pap tests and may increase the rate of detection of cervical neoplasia compared with CPT. Further study is necessary and warranted, since failure to detect cancer in a timely fashion affects ultimate cure rates, medical costs, quality of life, and perhaps medicolegal expenses. Although liquid-based thin layer cervical cytology is rapidly replacing the glass slide method throughout the United States, additional studies are also necessary to determine whether LBCC reduces the incidence of cervical cancer.

Acknowledgments

We appreciate the assistance of Cytyc Corporation in providing the supplies and grant support necessary for completion of this study.

We would like to thank the faculty and residents in the Family Medicine Center and OB/GYN Clinic who assisted with specimen collection, Jim Best for processing and interpreting cytologic specimens, Aisha Lavin for data management assistance, and April Dean for manuscript preparation.