Comparative study of the ThinPrep Pap test and conventional cytology results in a Canadian cohort

Objective:  To compare the frequency of Pap test results in a prospective series of direct to vial ThinPrep tests to a cohort of conventionally prepared tests. To follow‐up all test results for a minimum of 2 years and assess performance based on this outcome. Methods:  All women presenting for either routine screening or colposcopic examination in 2001 were enrolled in the ThinPrep cohort. A similar, population of conventionally prepared tests was extracted from the year 2000 laboratory data. Information on all concurrent and follow‐up cervical specimens over the ensuing 2 years was retrieved. Results:  The ThinPrep cohort comprised 2288 Pap tests and the conventional, 2211. The frequency of normal [within normal limits (WNL) and benign cellular changes (BCC)] results in the ThinPrep cohort was 6% lower and the frequency of abnormal [≥atypical squamous cells of undetermined significance (ASCUS)] results was 6.8% higher. Respective ThinPrep and conventional cohort results were 1156 (51%) and 1291 (58%) WNL, 625 (27%) and 561 (25%) BCC, 101 (4%) and 65 (3%) ASCUS, 21 (1%) and 2 (0.1%) atypical glandular cells of undetermined significance, 301 (13%) and 224 (10%) low‐grade squamous intraepithelial lesion (LSIL), and 74 (3%) and 40 (2%) high‐grade SIL (HSIL) ( P  < 0.0001). Follow‐up was available for nearly 80% of each cohort. LSIL or higher was confirmed in 57.5% ( n  = 266) of the abnormal ThinPrep and 60.9% ( n  = 190) of the abnormal conventional tests. The ThinPrep yield of confirmed tests however was almost 50% higher than the conventional test. Conclusion:  In this population, ThinPrep was superior to the conventional Pap test.