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Inappropriate calibration and optimisation of pan-keratin (pan-CK) and low molecular weight keratin (LMWCK) immunohistochemistry tests: Canadian Immunohistochemistry Quality Control (CIQC) experience
  1. Maria Copete1,
  2. John Garratt2,
  3. Blake Gilks3,
  4. Dragana Pilavdzic4,
  5. Richard Berendt5,6,
  6. Gilbert Bigras5,6,
  7. Sarah Mitchell5,6,
  8. Leslie Ann Lining1,
  9. Carol Cheung7,
  10. Emina E Torlakovic1,7
  1. 1University of Saskatchewan, Saskatoon, Saskatchewan, Canada
  2. 2Lions Gate Hospital, Vancouver, British Columbia, Canada
  3. 3University of British Columbia, Vancouver, British Columbia, Canada
  4. 4General Jewish Hospital, McGill University, Montreal, Quebec, Canada
  5. 5University of Alberta, Edmonton, Alberta, Canada
  6. 6Cross Cancer Institute, Edmonton, Alberta, Canada
  7. 7University Health Network, University of Toronto, Toronto, Ontario, Canada
  1. Correspondence to Dr Emina E Torlakovic, Department of Pathology, Toronto General Hospital, University Health Network, University of Toronto, 200 Elizabeth Street, Toronto, ON, M5G 2C4, Canada; emina.torlakovic{at}


Aims Pan-cytokeratin (pan-CK) and low molecular weight cytokeratin (LMWCK) tests are the most common immunohistochemistry (IHC) tests used to support evidence of epithelial differentiation. Canadian Immunohistochemistry Quality Control (CIQC), a new provider of proficiency testing for Canadian clinical IHC laboratories, has evaluated the performance of Canadian IHC laboratories in two proficiency testing challenges for both pan-CK and LMWCK.

Methods CIQC has designed a 70-sample tissue microarray (TMA) for challenge 1 and a 30-sample TMA for challenge 2. There were 13 participants in challenge 1, and 62 in challenge 2. All results were evaluated and scored by CIQC assessors and compared with reference laboratory results.

Results Participating laboratories often produced false-negative results that ranged from 20% to 80%. False-positive results were also detected. About half of participating clinical laboratories have inappropriately calibrated IHC tests for pan-CK and LMWCK, which are the most commonly used markers for demonstration of epithelial differentiation. The great majority of laboratories were not aware of the problem with calibration of pan-CK and LMWCK tests because of inappropriate selection of external positive controls and samples for optimisation of these tests. Benign liver and kidney are the most important tissues to include as positive controls for both pan-CK and LMWCK.

Conclusions Participation in external quality assurance is important for peer comparison and proper calibration of IHC tests, which is also helpful for appropriate selection of positive control material and material for optimisation of the tests.

  • Immunohistochemistry
  • quality assurance

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  • Funding Canadian Partnership Against Cancer (CPAC).

  • Competing interests None.

  • Provenance and peer review Not commissioned; externally peer reviewed.