Cervical cytology external and internal quality assurance: a comparative appraisal.

Introduction The National Health Service Cervical Screening Programme (NHSCSP) requires purchasers to ensure that laboratories are participating in appropriate external quality assessment schemes.' Laboratory providers must also show evidence in their business plans of active participation in both external and internal quality assurance programmes.2 However, little information is available on the comparative value of the different methods of quality assurance. As Chairman of the Trent Regional Gynaecological Cytology External Quality Assessment Committee I am involved in the monitoring of cytoscreener performance. This article describes a series of events which permitted an appraisal of external and internal quality assurance methods. The findings are relevant to quality assurance in the NHSCSP. To maintain confidentiality, the cytopathology department is kept anonymous.