When can odds ratios mislead?

Abstract

Guidelines for cervical screening await scientific evaluationEditor-In a news item about cervical screening in England 1 Wise refers to a report by the National Audit Office. 2 The office is particularly critical of serious failings in the interpretation of cervical smears in a small number of laboratories.The laboratory at the Hospital of St Cross in Rugby is included among these laboratories.In fact, a massive rescreening exercise at the hospital did not find any serious errors of interpretation, and the original reports were considered to be substantially correct and within the accepted operating limits of the smear test.The National Audit Office and the public assume that any deviation from the national guidelines for reporting rates represents mistakes by the laboratory.It is therefore interesting that, although the results at the hospital in Rugby were outside these guidelines, no serious errors were identified.This raises the question of whether the guidelines are an appropriate measure of laboratory performance.The guidelines themselves have come under considerable criticism in the pathology literature because of the lack of scientific evidence on which they are based. 3 One of their own authors has been particularly outspoken on the subject. 4 Though some of these arguments may seem of academic interest, cytology departments are being forced to close or merge as a result of the guidelines, which await scientific evaluation.Many staff feel threatened by the prescriptive way in which the guidelines have been introduced and applied and by the lack of understanding by the lay public and media of the limitations of the smear test.The incidence of and mortality from cervical cancer in the United Kingdom have shown accelerated falls since the introduction of organised screening (J Patnick, NHS cervical screening programme information sheet, 21 Nov 1996).Of course there is room for improvement, but it is ironic that the publication of various reports designed to improve the service could lead to its eventual collapse through staff leaving the profession.