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Evidence summaries

Liquid-Based Versus Conventional Cervical Cytology

Liquid-based cytology appears to be as effective as conventional cervical cytology. Level of evidence: "B"

A health technology assessment report evaluating liquid-based cytology (LBC) in cervical cancer screening in terms of efficacy, undesired effects, and costs included 3 RCTs with complete verification of test positives (n=143 612). No longitudinal study was available. There is currently no clear evidence that LBC increases the sensitivity of cytology and even less that its introduction increases the efficacy of cervical screening in preventing invasive cancers. The Italian randomised study NTCC showed a decrease in specificity, which was not observed in the other two RCTs available. In addition, the 2008 meta-analysis observed a reduction - even if minimal - in specificity just at the ASC-US cytological cut-off, but also a remarkable heterogeneity between studies. These results suggest that the effect of LBC on specificity is variable and plausibly related to the local style of cytology interpretation. There is evidence that LBC reduces the proportion of unsatisfactory slides, although the size of this effect varies remarkably. LBC needs shorter time for interpretation than conventional cytology. However, in the Italian situation, savings obtained from this time reduction and from the decreased number of repeats due to unsatisfactory slides were not currently sufficient to compensate the cost increase due to the prices currently applied by producers and to a possible greater number of colposcopies caused by LBC.

Fifty-six primary studies 1 on liquid-based cytology relative to conventional cytology were reviewed and assessed with strict methodological criteria. Only one small study was an RCT and five were satisfactorily designed. The median difference in the percentage of unsatisfactory slides between liquid-based cytology and conventional cytology was 0.17%. The classification of high-grade squamous epithelial lesion varied according to study quality (p=0.04), with conventional cytology classifying more slides in this category than did liquid-based cytology in high-quality studies only. In medium-quality (n=30) and high-quality studies (n=3), liquid-based cytology classified more slides as atypical squamous cells of unknown significance than did conventional cytology when compared with low-quality studies (n=17; p=0.05). Only four studies provided sufficient verified data to allow estimation of sensitivity and specificity and comparison of test accuracy.

Comment: The quality of evidence is downgraded by limitations in study quality.

    References

    • Davey E, Barratt A, Irwig L, Chan SF, Macaskill P, Mannes P, Saville AM. Effect of study design and quality on unsatisfactory rates, cytology classifications, and accuracy in liquid-based versus conventional cervical cytology: a systematic review. Lancet 2006 Jan 14;367(9505):122-32. [PubMed]
    • Ronco G, Confortini M, Maccallini V et al. [Health technology assessment report. Use of liquid-based cytology for cervical cancer precursors screening]. Epidemiol Prev 2012;36(5 Suppl 2):e1-e33. [PubMed]

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