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Prolonging fixation time of an alternative fixative to formalin for dermatological samples using standard laboratory protocols
  1. Julie Smith1,
  2. Cláudia Sofia Antunes Angélica Faria2,
  3. Camilla Christine Qvist3,
  4. Linea C Melchior3,
  5. Thomas Lauridsen3,4
  1. 1 Department of Technology, Faculty of Health and Technology, University College Copenhagen, Copenhagen, Denmark
  2. 2 Lisbon School of Health Technology, Polytechnic Institute of Lisbon, Lisbon, Portugal
  3. 3 Department of Pathology, Copenhagen University Hospital (Rigshospitalet), Copenhagen, Denmark
  4. 4 Department of Pathology, Zealand University Hospital, Roskilde, Denmark
  1. Correspondence to Dr Julie Smith, Department of Technology, University College Copenhagen, Copenhagen 2200, Denmark; jusi{at}


Aims Though formalin remains to be the gold standard fixative in pathology departments, analytical challenges persist for nucleic acid evaluations. In our laboratory, formalin fixation of skin samples in particular impairs diagnostic accuracy and demands repetition of biopsies and analytical procedures. PAXgene Tissue Systems may be an alternative; however, according to manufacturer specifications it only allows fixation for 48 hours before having to add a stabiliser. This may be a challenge in laboratories, which are closed in weekends and bank holidays. Our aim was to validate this alternative fixative for dermatological samples with prolonged fixation times using standard laboratory protocols developed for formalin-fixed specimens. We compared the results with gold standard formalin fixation.

Methods Skin specimens were formalin or PAXgene fixed for either 2 hours, 24 hours, 3 days or 7 days, paraffin-embedded, analysed and scored by observers.

Results Generally, formalin outperformed PAXgene fixation in H&E stains and fluorescence in situ hybridisation (FISH), but both seem usable for diagnostics. Time of PAXgene fixation did not have an impact on alcian blue-Van Gieson (ABVG), H&E (p=0.48), nor immunohistochemistry (p=0.74). There was a tendency towards best PAXgene performance at 24 hours of fixation for FISH, and for DNA integrity analysis 24 hours or 3 days.

Conclusions Prolonging PAXgene fixation time to 3 days before adding stabiliser does not seem to have major impact on performance of general diagnostic analysis, but our preliminary results show optimisation of internal protocols are needed. PAXgene is an expensive alternative and may be confined to some dermatological samples.

  • diagnostic techniques and procedures
  • immunohistochemistry
  • medical laboratory science
  • skin
  • molecular biology

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  • Handling editor Runjan Chetty.

  • Contributors All authors have been part of planning, conducting and reporting of this work.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Competing interests None declared.

  • Patient consent for publication Not required.

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

  • Data availability statement Data are available upon reasonable request. All data relevant to the study are included in the article. For additional information please contact corresponding author.