Level 1: Likely reliable evidence
Liquid-based cytology is a commonly used method for cervical cancer screening, but new evidence suggests that ThinPrep, a liquid-based test, is no more effective than conventional cytology. In a cluster-randomized trial conducted in 246 clinics in the Netherlands, ThinPrep was compared with conventional cytology for cervical cancer screening in 89,784 women aged 30-60 years (Obstet Gynecol. 2008;112:1327-1324). Although the liquid-based test resulted in fewer unsatisfactory results, there were no significant differences in the detection of abnormalities between the two tests in analyses performed at two independent laboratories. For each test, the rate of atypical squamous cells of undetermined significance was 2%-4%, low-grade squamous intraepithelial lesions about 1%, and high-grade squamous intraepithelial lesions 0.5%-0.8%. These results are consistent with an earlier systematic review (Obstet Gynecol. 2008;111:167-177) and an earlier randomized trial (BMJ. 2007;335:28-34; available at www.bmj.com/cgi/content/full/335/7609/28, accessed May 12, 2009). Liquid-based cytology is more expensive than conventional cytology, but it does provide the added ability to test for human papillomavirus (including reflexive testing of abnormal samples), gonorrhea, and chlamydia from the same sample. Whether this benefit warrants the increased cost will depend on a number of factors that may vary across different practice environments.