Evaluation of the ThinPrep Pap test in clinical practice. A seven-month, 16,314-case experience in northern Vermont.

OBJECTIVE: To compare the cytologic diagnoses and specimen adequacy of the ThinPrep Pap Test with historical data within a distinct patient population to assess test performance and its impact on clinical practice. STUDY
DESIGN: A total of 16,314 ThinPrep Pap tests were processed and evaluated at Fletcher Allen Health Care over a seven-month period. A subset of 8,574 tests from a selected provider group (cohort) was compared to the historical conventional cervical cytologic smear data from the cohort population for both cytologic diagnoses and specimen adequacy. The cohort consisted of 12 practice groups, including 60 physicians and providers, utilizing the ThinPrep Pap Test as their primary cervical cancer screening sampling technique. Cytologic diagnoses and specimen adequacy were classified using the Bethesda system.
RESULTS: Using a three-tiered diagnostic system similar to the Cytyc clinical trials (within normal limits [WNL], atypical squamous cells of undetermined significance [ASCUS]/atypical glandular cells of undetermined significance [AGUS] and low grade squamous intraepithelial lesion and higher [LSIL]+), the ThinPrep method increased the percentage of cases that could be definitively diagnosed as WNL by 1.71%, lowered the percentage of ambiguous or borderline cases diagnosed as ASCUS/AGUS by 26.59% and increased the percentage of cases diagnostic of LSIL+ by 52.15% in the cohort population. Further subdivision by the Bethesda classification showed that the identification of infectious agents increased 25.51% and the detection of high grade squamous intraepithelial lesion/carcinoma increased 55.14%. Concurrently, cases reported as benign cellular changes (reactive/reparative) decreased 23.1%, and the percentage of cases reported as unsatisfactory/"limited by ..." was reduced 52.71%. Histologic correlation of cases reported as squamous intraepithelial lesion revealed that the percentage of patients with subsequent benign biopsies was reduced by 31.7% utilizing the ThinPrep technique. Further, the percentage of ThinPrep patients with histologically confirmed cervical intraepithelial neoplasia (CIN) 1 and CIN 2/3 increased by 16.3% and 9.3%, respectively.
CONCLUSION: Implementation of the ThinPrep Pap Test resulted in statistically significant improvements in both diagnostic yield and specimen adequacy, as seen by others in clinical trials. Comparison of results to historical data within a cohort population reinforced earlier data and lent further support to the claim that the ThinPrep Pap Test is "significantly more effective" than the conventional smear in clinical practice.