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  3. Accuracy of reading liquid based cytology slides using the ThinPrep Imager compared with conventional cytology: prospective study
Research

Accuracy of reading liquid based cytology slides using the ThinPrep Imager compared with conventional cytology: prospective study

BMJ 2007; 335 doi: https://doi.org/10.1136/bmj.39219.645475.55 (Published 05 July 2007) Cite this as: BMJ 2007;335:31
  1. Elizabeth Davey, research fellow1,
  2. Jefferson d'Assuncao, research officer1,
  3. Les Irwig, professor of epidemiology1,
  4. Petra Macaskill, associate professor of biostatistics1,
  5. Siew F Chan, statistical research officer1,
  6. Adele Richards, cytology manager2,
  7. Annabelle Farnsworth, medical director2
  1. 1Screening and Test Evaluation Program, School of Public Health, University of Sydney, NSW 2006, Australia
  2. 2Cytology Department, Douglass Hanly Moir Pathology, North Ryde, NSW, Australia
  1. Correspondence to: E Davey daveye{at}health.usyd.edu.au
  • Accepted 3 May 2007

Abstract

Objective To compare the accuracy of liquid based cytology using the computerised ThinPrep Imager with that of manually read conventional cytology.

Design Prospective study.

Setting Pathology laboratory in Sydney, Australia.

Participants 55 164 split sample pairs (liquid based sample collected after conventional sample from one collection) from consecutive samples of women choosing both types of cytology and whose specimens were examined between August 2004 and June 2005.

Main outcome measures Primary outcome was accuracy of slides for detecting squamous lesions. Secondary outcomes were rate of unsatisfactory slides, distribution of squamous cytological classifications, and accuracy of detecting glandular lesions.

Results Fewer unsatisfactory slides were found for imager read cytology than for conventional cytology (1.8% v 3.1%; P<0.001). More slides were classified as abnormal by imager read cytology (7.4% v 6.0% overall and 2.8% v 2.2% for cervical intraepithelial neoplasia of grade 1 or higher). Among 550 patients in whom imager read cytology was cervical intraepithelial neoplasia grade 1 or higher and conventional cytology was less severe than grade 1, 133 of 380 biopsy samples taken were high grade histology. Among 294 patients in whom imager read cytology was less severe than cervical intraepithelial neoplasia grade 1 and conventional cytology was grade 1 or higher, 62 of 210 biopsy samples taken were high grade histology. Imager read cytology therefore detected 71 more cases of high grade histology than did conventional cytology, resulting from 170 more biopsies. Similar results were found when one pathologist reread the slides, masked to cytology results.

Conclusion The ThinPrep Imager detects 1.29 more cases of histological high grade squamous disease per 1000 women screened than conventional cytology, with cervical intraepithelial neoplasia grade 1 as the threshold for referral to colposcopy. More imager read slides than conventional slides were satisfactory for examination and more contained low grade cytological abnormalities.

Footnotes

  • We thank Rodney Ecclestone, Paul Jelfs, Yeqin Zuo, and staff of the Cancer Institute of New South Wales for their help in providing access to data in the New South Wales Pap test register; Colin Goldschmidt (Sonic Healthcare); the pathologists and cytologists of Douglass Hanly Moir Pathology for their very helpful contribution; staff at other pathology laboratories for their invaluable assistance in providing histology slides for rereading; and Alexandra Barratt for constructive comments on a draft of this paper.

  • Contributors: ED participated in the design, development, and conduct of the study; entered data; coordinated analyses; wrote drafts of the paper; and reviewed the paper. She is guarantor. LI developed the methodological approach to the study and designed the study, supervised the conduct of the study, reviewed analyses, interpreted results, and participated in writing and reviewing the paper. PM developed the methodological approach to the study, designed the study; directed, carried out, and reviewed analyses; interpreted results, and participated in writing and reviewing the paper. SFC had a major role in data management and carried out analyses. JD'A assisted in data management and statistical analyses. AR participated in the development of the study design and managed the day to day running of the study, collection of data, and transference of data; and participated in the reviewing of the paper. AF initiated the study; participated in the development of the methodological approach and study design, the day to day running of the study, the collection and transference of data, rereading of the histology slides, over-viewing the analysis of the data, and writing and reviewing the paper.

  • Funding: This work was supported in part by grants (Nos 211205 and 402764) from the National Health and Medical Research Council, Australia. The funding source had no involvement in the study design, data collection, analysis, data interpretation, writing of the report, or decision to publish this work.

  • Ethical approval: The study was approved by the ethics committee of the Cancer Institute of New South Wales and by the University of Sydney Human Research Ethics Committee.

  • Accepted 3 May 2007
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