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Liquid-based cytology (LBC) has rapidly become the preferred method for preserving and analyzing cellular material collected from the transformation zone of the uterine cervix with a spatula or a brush. With LBC, cells are first transferred into a liquid fixative and then concentrated and uniformly spread on slides for evaluation. LBC is much more costly than conventional cervical cytology, but is it better?
In a systematic review, investigators identified nine studies in which both conventional and liquid-based methods were evaluated; they all included validation of results by colposcopy and biopsy. The relative sensitivity and the specificity, using high-grade or low-grade squamous intraepithelial lesions as cutoff points, did not differ between the two techniques. Specificity was lower (false-positive rate was higher) for LBC when atypical squamous cells of undetermined significance were used as the cutoff.
Arbyn M et al. Liquid compared with conventional cervical cytology: A systematic review and meta-analysis. Obstet Gynecol 2008 Jan; 111:167.
Sawaya GF. Evidence-based medicine versus liquid-based cytology. Obstet Gynecol 2008 Jan; 111:2.
Comment
Even though the U.S. Preventive Services Task Force currently considers evidence to be insufficient to recommend a method for performing Pap smears, liquid-based cytology has become the standard. Insurance companies that will pay less than the cost for conventional cytology willingly have absorbed the cost of this more expensive approach. One reason for this method’s popularity is that it allows human papillomavirus (HPV) testing to be performed; another reason could be effective marketing. Time will tell whether HPV testing should replace histologic cytology for screening, but, as an editorialist notes, we should remain skeptical about liquid-based cytology if it increases false-positives and leads to additional testing and emotional concerns for women with mild abnormalities.