Liquid-based versus conventional cervical cytology

Abstract

If Elizabeth Davey and colleagues “saw no evidence that liquid-based cytology (LBC) reduced the proportion of unsatisfactory slides” (Jan 14, p 122),1Davey E Barratt A Irwig L et al.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; 367: 122-132Summary Full Text Full Text PDF PubMed Scopus (238) Google Scholar they must have looked in the wrong place. The reduction in inadequate smears associated with the introduction of LBC in UK laboratories has been striking. In 2002–03, 2003–04, and 2004–05, the three laboratories in England that use LBC screened more than 400 000 slides and had an overall inadequate rate of 0·8% (1·5% or less annually in each laboratory).2Department of HealthCervical screening programme, England: 2002–03. DoH, London2003Google Scholar, 3Department of HealthCervical screening programme, England: 2003–04. DoH, London2004Google Scholar, 4NHS Health and Social Care Information CentreCervical screening programme, England: 2004–05. NHS HSCIC, London2005Google Scholar Before the introduction of LBC, all three had rates of more than 7·5%. One might have thought that these changes were due to the retraining associated with the introduction of the new technology. Here data from the pilot studies in Wales are most revealing.5Cervical Screening WalesLiquid based cytology—pilot project: project report. Velindre NHS Trust, Cardiff2003Google Scholar As in England, the inadequate rates for the LBC samples, using recorded working criteria, fell from more than 7·5% to less than 2·0%. Further, three of the laboratories involved also continued to screen conventional smears during the pilot. The inadequacy rates of conventional smears fell after smear takers had received LBC training, but remained at 6·6%. Thus their training had an effect, but the major effect was due to the change in technology. Davey and colleagues also did not take into account the different definitions of unsatisfactory or inadequate use. If, because of a less stringent definition, the inadequacy rates of conventional cytology are less than 1·5%, there is little room for improvement, and including such studies in a meta-analysis would dilute the effect seen in laboratories with a more stringent definition. We declare that we have no conflict of interest. Liquid-based versus conventional cervical cytology – Authors' replyNone of the responses to our systematic review challenges our methods or our most important finding, that we found no evidence that liquid-based cytology (LBC) is more accurate than conventional cytology. There are many reasons to convert to LBC if at least equivalent accuracy for the detection of important cervical disease can be shown. However, if it cannot, no reason, not even a reduction in unsatisfactory rate, is sufficient to justify the change. We found that few of the studies were designed and conducted well enough to assess accuracy properly, and the few that were showed no improvement by using LBC. Full-Text PDF