Comparison of staining adequacy between tissues stored in formalin and paraffin embedded blocks for prolonged duration.

Introduction: Tissues submitted for histopathological diagnoses are routinely fixed in formaldehyde fixative which facilitates tissue storage for the extended period of time for further investigation or research purpose. The literature has reliable data relating to immunohistochemistry and molecular studies done using tissue fixed in formalin for longer duration and in paraffin-embedded tissue blocks. We have attempted to evaluate staining adequacy of archival specimens using hematoxylin and eosin (H&E) and trichrome stains.

Methodology: We compared staining adequacy in tissues stored in formalin for a minimum period of 5 years labeled as long term fixed tissues (LFT) and corresponding 5-year-old paraffin-embedded tissue blocks of same cases available in the archives designated as old tissue blocks (OTB), along with freshly fixed tissues (FFT) used as controls. Fifty-one tissue sections in each study group were stained with H&E, Mallory's trichrome and Van Giesons' and microscopic evaluation was carried out using Research Microscope B × 51.

Results: Staining adequacy of the tissue sections was found to be superior in FFT, followed by OTB and LFT using all three stains. Staining for H&E, was found to be superior as compared to trichrome stains.

Conclusion: Trichrome stains were poorly demonstrated in LFT indicating the possible alteration in protein structure and tissue architecture in LFT whereas H&E, stained LFT specimens showed relatively good staining character. Hence, OTB proved to be better as compared to LFT in terms of staining quality and hence archiving tissue in paraffin embedded tissue blocks serve as valuable bio-bank and source for prospective studies.