Formalin-fixed, paraffin-embedded unstained archived diagnostic tissue sections are frequently exchanged between clinical laboratories for immunohistochemical staining. The manner in which such sections are prepared represents a type of preanalytical variable that must be taken into account given the growing importance of immunohistochemical assays, especially predictive and prognostic tests, in personalized medicine.
Recommendations were derived from review of the literature and expert consensus of the Canadian Association of Pathologists-Association canadienne des pathologists National Standards Committee for High Complexity Testing/Immunohistochemistry.
Relevant considerations include the type of glass slide on which to mount the unstained sections; the thickness of the tissue sections; the time from slide preparation to testing; the environment, particularly the temperature at which the unstained sections will be maintained prior to testing; the inclusion of on-slide positive control tissue where possible; and whether patient identifier(s) should be included on slide labels.
Clear communication between requesting and releasing laboratories will facilitate the proper preparation of unstained sections and also ensure that applicable privacy considerations are addressed.