Commercial Formalin Substitutes for Histopathology

We compared the performance of six commercial fixatives proposed to be formalin substitutes with the performance of buffered formalin, Clarke's ethanol-acetic acid, and ethanol, using rat liver, small intestine, and kidney. We investigated the rate of penetration, mode of fixation, extent of protein and structural immobilization, quality of histology and cellular structure following routine dehydration and paraffin embedding, and performance as a fixative for immunohistochemistry. Furthermore, we evaluated the effects of the various fixatives on ultrastructure. Only buffered formalin performed equally well on all tissues tested. While several of the commercial fixatives appeared to preserve liver tissue at 200, the preservation of kidney, intestinal villi, and smooth muscle was unacceptable. Histological distortion, cell shrinkage and vacuolization were prominent when the substitutes or ethanol were used. In contrast, these artifacts were found occasionally and to a minor degree when buffered formalin or Clarke's fixative were used. Immunohistochemistry demonstrated a total loss of low molecular weight antigen (serotonin) and patchy reactions for high molecular weight antigens for all fixatives except buffered formalin. The best immunostaining was obtained by combining formalin fixation with antigen retrieval. We conclude that none of the proposed commercial substitutes for buffered formalin are adequate for critical histology or histopathology.