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Best Tests March 2007

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Is liquid based cervical cytology better?

Conventional cervical cytology has been used for over 50 years, with very little change: a brush or spatula is used to remove cells from the endocervix which are smeared onto a glass slide. Recently, liquid based cytology (LBC) has become available. LBC differs from conventional methods in that the device used to collect cervical cells is rinsed or broken off into a vial of preservative liquid. A microscope slide is prepared by the laboratory. There has been increasing interest in the use of LBC methods as they have become FDA approved and have been adopted as the method of choice in a number of countries. In New Zealand two methods of LBC are available, ThinPrep and SurePath.

There has been conflicting reports on the performance of LBC over conventional cytology in many studies. A recent meta-analysis1 of more than 1.25 million slides concluded there was no evidence that LBC performed better than conventional cytology. The authors noted that many of the studies of LBC were of poor quality and large randomised controlled trials are needed. In New Zealand, conventional cervical cytology remains the method of choice for cervical cytology although the National cervical screening programme has acknowledged the potential advantages of LBC. In their draft guideline2 (final guideline due July 2007) they suggest that LBC may offer some advantages over conventional smears for women with:

  • Excessive cervical mucus, discharge or blood
  • Recurrent inflammatory smears
  • Recurrent unsatisfactory smears

References:

  1. Davey E, Barratt A, Irwig L, et al. Effect of study design and quality on unsatisfactory rates, cytology classifications, and accuracy in liquid-based versus conventional cervical cytology: a systematic review. Lancet 2006:367;122-32.
  2. National cervical screening programme. Proposed New Guidelines for the Management of Women with Abnormal Cervical Smears. October 2006.