Natural fixatives alternative to formalin in histopathology: A systematic review

Since constant long-term exposure to formaldehyde endangers the health of laboratory personnel, sugar-based natural products have become interesting alternative fixatives to formaldehyde because of their preservative and antibacterial properties. However, there are controversial findings on the fixative effects of natural fixatives. This study systematically reviews the evidence comparing natural fixatives' types, dilutions, fixative properties and staining quality in normal tissues and histopathological specimens.

A comprehensive search was performed for studies comparing the natural fixatives- and formaldehyde-fixed tissues using databases from inception to January 2022: PubMed, Ovid Medline and Google Scholar. Two independent reviewers did data extraction. The data were pooled for the type of natural fixatives, their concentrations and fixative qualities compared to formaldehyde.

Fifteen studies were included in this systematic review. Nine studies used one natural fixative with different dilutions, while six used several natural fixatives to compare their fixative properties with formaldehyde. The most used natural fixative was honey (n = 12) followed by jaggery (n = 8), sugar (n = 3) and others (n = 1). Honey showed the most promising results in fixation and staining, which are compatible with formalin. Jaggery and sugar also showed the possibility of replacing formaldehyde in tissue fixation and staining in smaller tissue samples.

Natural fixatives showed promising results in tissue fixation. However, optimising the concentrations and conditions of natural fixatives is difficult because of the different chemical constituents and production steps. More comprehensive studies are necessary for application.