COMMERCIAL FORMALIN SUBSTITUTES FOR HISTOPATHOLOGY

We compared the performance of six commercial fixatives proposed to be formalin substitutes with the performance of buffered formalin, Clark e's ethanol-acetic acid, and ethanol, using Fat liver, small intestine , and kidney. We investigated the rate of penetration, mode of fixatio n, extent of protein: and structural immobilization, quality of histol ogy and cellular structure following routine dehydration and paraffin embedding, and performance as a fixative for immunohistochemistry. Fur thermore, we evaluated the effects of the various fixatives on ultrast ructure. Only buffered formalin performed equally well on all tissues tested. While several of the commercial fixatives appeared to preserve liver tissue at 200 x, the preservation of kidney, intestinal villi, and smooth muscle was unacceptable. Histological distortion, cell shri nkage and vacuolization were prominent when the substitutes or ethanol were used. In contrast, these artifacts were found occasionally and t o a minor degree when buffered formalin or Clarke's fixative were used . Immunohistochemistry demonstrated a total loss of low molecular weig ht antigen (serotonin) and patchy reactions for high molecular weight antigens for all fixatives except buffered formalin. The best immunost aining was obtained by combining formalin fixation with antigen retrie val. We conclude that none of the proposed commercial substitutes for buffered formalin are adequate for critical histology or histopatholog y.