ThinPrep Pap Test: performance and biopsy follow-up in a university hospital.

Abstract

The ThinPrep Pap Test (TP), a liquid-based cervical cytology preparation, was approved for use in the U.S. in 1996. The purpose of this study was to compare TP performance and biopsy follow-up studies with a similar population of high risk patients sampled by conventional Papanicolaou (Pap) smear (CS). Diagnostic and specimen adequacy interpretations for 2727 TP direct-to-vial Pap tests from a high risk university hospital practice were compared with 5000 CS preparations from the same physicians taken 1 year previously. Biopsy follow-up studies for the categories of squamous intraepithelial lesion (SIL), carcinoma, and atypical squamous cells of undetermined significance (ASCUS) for each time period and technique were contrasted. The SIL/carcinoma detection rate increased from 7.7% to 10.5% (P < 0.01) and the ASCUS rate decreased from 12.5% to 6.9% (P < 0.01); the percentage of satisfactory but limited specimens decreased from 19.4% to 10.5% (P < 0.01). Low grade SIL cases increased by 57% (P < 0.01) whereas the 26% increase in high grade SIL cases was not statistically significant. Greater than 90% of ungraded SIL, high grade SIL, and carcinoma cases had abnormal biopsies by both the TP and CS methods. The number of biopsy-confirmed high grade dysplasias and carcinomas was similar in the two groups. A low grade SIL detected by TP was less likely to have an abnormal biopsy (70% vs. 85% for CS). Nevertheless, the 57% increase in low grade SIL diagnoses by TP resulted in more TP patients with dysplastic biopsy diagnoses. Follow-up studies for ASCUS cases diagnosed by either TP or CS were similar, and 21-24% of patients eventually were found to have dysplasia. The TP technique appears to lead to the increased detection of low grade SIL lesions, decreased satisfactory but limited samples, and fewer equivocal specimens. No increase in biopsy-confirmed high grade dysplasias and carcinomas was found. Follow-up studies for the ASCUS category were nearly identical to those for CS.