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Doubts over new smear test

Liquid-based cytology is no better than conventional pap smears for cervical screening, a major new systematic review concludes.

The study, published in The Lancet this week, found the technique did not cut the number of unsatisfactory slides or improve detection of high-grade lesions.

The findings cast doubt on the rationale behind the £10 million plan to switch to liquid-based cytology in the NHS cervical screening programme.

The switchover, due to be complete by 2008, was recommended by NICE to reduce the number of 'inadequate' results and make slides easier to read. But the new Australian study, of data from 1.25 million slides in 56 studies comparing the two techniques, found liquid-based cytology was no better.

The median difference in the proportion of unsatisfactory slides was just 0.17 per cent between the two techniques. In higher-quality studies, liquid-based cytology detected fewer high-grade squamous intraepithelial lesions than pap smears.

The researchers also found very few studies were adequately powered to compare performance of the two tests.

Study leader Dr Elizabeth Davey, research fellow at the Screening and Test Evaluation Program in Sydney, Australia, said: 'The evidence does not lend support to a conclusion that liquid-based cytology is better than conventional cytology. Liquid-based cytology did not reduce the proportion of unsatisfactory slides.'

In an accompanying commentary, Dr Jorg Obwegeser, gynaecologist and cytologist at a private clinic in Zurich, Switzerland, criticised the rush to switch to liquid-based cytology. He said policymakers in England and Scotland had been 'convinced this technique would improve their problem of a very high unsatisfactory rate'­ despite evidence to the contrary.

But Dr Anne Szarewski, clinical consultant at Cancer Research UK, insisted large-scale pilot studies had shown liquid-based cytology reduced unsatisfactory smears: 'The conclusions drawn do not tally with the experience of using liquid-based cytology screening in the UK,' she said.

Professor Mike Campbell, professor of medical statistics at the University of Sheffield and member of the NICE committee on liquid-based cytology, said even if it was no better, in the long-term it would be cheaper to run.

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