The impact of the introduction of liquid based cytology on the variation in the proportion of inadequate samples between GP practices

Routinely collected cervical cytology data was obtained for all general practices in two localities in South Staffordshire for periods before and after the introduction of liquid based cytology. Control charts of the proportion of inadequate smears were plotted for the practices stratified by laboratory. A standardised measure of variation for all of the practices in each laboratory and each time period was also calculated.Following the introduction of liquid based cytology the overall proportion of inadequate samples in the two localities fell from 11.8 to 1.3% (p < 0.05). This fall was associated with a reduction in the average variation between the GP practices in the two localities from 1.6 to 1.0 standard deviations. There has also been a reduction in the number of practices showing special cause variation from eight to one following the introduction of liquid based cytology.A reduction in the proportion of inadequate samples has been realised in these localities. The reduction in the overall proportion of inadequate samples has also been accompanied by a reduction in variation between GP practices.In 2005/06 3.6 million women were screened for cervical cancer in England, 3.36 million following a formal invitation from the screening programme, generating just under 4.0 million cervical smears [1]. Women who have a smear which is identified as inadequate by the reporting cytology laboratory must be retested, in line with national guidelines, and women who have three successive inadequate smears are referred for colposcopy [2]. Inadequate smears are a source of avoidable distress to women, and a potential waste of resources in general practices, clinics and cytology laboratories [2].A study we undertook in South Staffordshire in 2000–01 identified two sources of variation in the proportion of inadequate smears; that associated with laboratories and that associated with GP practices [3]. Our study showed that there was wide variation in the proportion of inadequat