Human Papillomavirus testing and liquid-based cytology

Human papillomavirus (HPV) testing was more sensitive than traditional Pap smears at detecting precancerous lesions of the cervix, a study in the Journal of the National Cancer Institute reports.

A new, liquid-based form of the Pap test marginally improved sensitivity but also produced more false positives.

Previous studies have shown that searching for a precancerous cervical lesion called cervical intraepithelial neoplasia with an HPV test is more sensitive but also has more false positives than conventional pap smears, where doctors look for abnormal cells on a slide. Despite the widespread use of newer Pap technology called liquid-based cytology, where doctors first immerse the Pap sample in a solution before looking at the cells, its accuracy is not clearly defined. Some scientists suggest there is a need to understand what combination of tests increases sensitivity while keeping the number of false positives acceptable.

Guglielmo Ronco, M.D., Ph.D., of CPO Piemonte in Torino, Italy, and colleagues set up a randomized controlled trial that screened over 33,000 women for cervical cancer, half with conventional pap smears and the other half with HPV tests and liquid-based cytology. Women with abnormal cells from either Pap test or a positive HPV result were further examined by a technique called colposcopy, where doctors use a magnifying instrument to get a detailed view of the cervix.

The authors found that HPV testing combined with liquid-based cytology led to a 47% increase in sensitivity compared to conventional pap smears, but increased the chance of false positives by 60%. HPV testing alone increased sensitivity by more than 40%, with a smaller decrease in specificity (25% or 42%, depending on the type of test used). Liquid-based cytology did not show greater sensitivity than conventional pap smears, but increased the number of false positives.

The authors write, "HPV testing alone was more sensitive than conventional [pap smears] among women 35-60 years old. Adding liquid-based cytology improved sensitivity only marginally but increased false positives."