title: A study of cellular counting to determine minimum thresholds for adequacy for liquid-based cervical cytology using a survey and counting protocol.
abstract: BACKGROUND
  Liquid-based cytology (LBC) for cervical screening would benefit from laboratory practice guidelines that define specimen adequacy for reporting of slides. The evidence base required to define cell adequacy should incorporate both ThinPrep™ (TP; Hologic, Inc., Bedford, MA, USA) and SurePath™ (SP; BD Diagnostics, Burlington, NC, USA), the two LBC systems used in the UK cervical screening programmes.
  
  
  OBJECTIVE
  The objectives of this study were to determine (1) current practice for reporting LBC in England, Wales and Scotland, (2) a reproducible method for cell counting, (3) the cellularity of slides classified as inadequate, negative or abnormal and (4) the impact of varying cellularity on the likelihood of detecting cytological abnormalities.
  
  
  METHODS
  The study involved four separate arms to pursue each of the four objectives. (1) A questionnaire survey of laboratories was conducted. (2) A standard counting protocol was developed and used by three experienced cytopathologists to determine a reliable and reproducible cell counting method. (3) Slide sets which included a range of cytological abnormalities were each sent to three laboratories for cell counting to study the correlation between cell counts and reported cytological outcomes. (4) Dilution of LBC samples by fluid only (unmixed) or by dilution with a sample containing normal cells (mixed) was performed to study the impact on reporting of reducing either the total cell count or the relative proportion of abnormal to normal cells.
  
  
  METHODS
  The study was conducted within the cervical screening programmes in England, Wales and Scotland, using routinely obtained cervical screening samples, and in 56 participating NHS cervical cytology laboratories.
  
  
  METHODS
  The study involved only routinely obtained cervical screening samples.
  
  
  METHODS
  There was no clinical intervention.
  
  
  METHODS
  The main outcome measures were (1) reliability of counting method, (2) correlation of reported cytology grades with cellularity and (3) levels of detection of abnormal cells in progressively diluted cervical samples.
  
  
  RESULTS
  Laboratory practice varied in terms of threshold of cellular adequacy and of morphological markers of adequacy. While SP laboratories generally used a minimum acceptable cell count (MACC) of 15,000, the MACC employed by TP laboratories varied between 5000 and 15,000. The cell counting study showed that a standard protocol achieved moderate to strong inter-rater reproducibility. Analysis of slide reporting from laboratories revealed that a large proportion of the samples reported as inadequate had cell counts above a threshold of 15,000 for SP, and 5000 and 10,000 for TP. Inter-rater unanimity was greater among more cellular preparations. Dilution studies demonstrated greater detection of abnormalities in slides with counts above the MACC and among slides with more than 25 dyskaryotic cells.
  
  
  CONCLUSIONS
  Variation in laboratory practice demonstrates a requirement for evidence-based standards for designating a MACC. This study has indicated that a MACC of 15,000 and 5000 for SP and TP, respectively, achieves a balance in terms of maintaining sensitivity and low inadequacy rates.
  
  
  CONCLUSIONS
  The findings of this study should inform the development of laboratory practice guidelines.
  
  
  BACKGROUND
  The National Institute for Health Research Health Technology Assessment programme.
authors.affiliation: Institute of Cancer Sciences, St. Mary's Hospital, University of Manchester, Manchester, UK.
authors.forename: Henry C
authors.initials: HC
authors.lastname: Kitchener
authors.affiliation: Institute of Population Health, University of Manchester, Manchester, UK.
authors.forename: Matthew
authors.initials: M
authors.lastname: Gittins
authors.affiliation: Cytology Department, Clinical Sciences Building, Central Manchester University Hospitals NHS Foundation Trust, Manchester, UK.
authors.forename: Mina
authors.initials: M
authors.lastname: Desai
authors.affiliation: Department of Histology and Cytology, Royal Hallamshire Hospital, Sheffield Teaching Hospitals NHS Foundation Trust, Sheffield, UK.
authors.forename: John H F
authors.initials: JH
authors.lastname: Smith
authors.affiliation: Stepping Hill Hospital, Stockport NHS Foundation Trust, Stockport, UK.
authors.forename: Gary
authors.initials: G
authors.lastname: Cook
authors.affiliation: Institute of Population Health, University of Manchester, Manchester, UK.
authors.forename: Chris
authors.initials: C
authors.lastname: Roberts
authors.affiliation: Liverpool Women's Hospital, Liverpool, UK.
authors.forename: Lesley
authors.initials: L
authors.lastname: Turnbull
mesh_terms: D002452:Cell Count / Q000379:methods / Q000592:standards; D003584:Cytological Techniques / Q000379:methods* / Q000592:standards*; D005260:Female; D006801:Humans; D012015:Reference Standards; D015203:Reproducibility of Results; D011795:Surveys and Questionnaires; D013673:Technology Assessment, Biomedical; D006113:United Kingdom; D002583:Uterine Cervical Neoplasms / Q000175:diagnosis; D014626:Vaginal Smears / Q000379:methods / Q000592:standards; D002578:Uterine Cervical Dysplasia / Q000175:diagnosis