Turmeric as a counterstain in histology

Histologic stains which identify specific tissue and cellular components are a staple of all diagnostic pathology laboratories. Histotechnology scientists are constantly attempting to find methods and reagents which are specific, simple to use, and cost effective. Turmeric (Curcuma longa) is a yellow spice readily available in grocery stores and is inexpensive. Previously, turmeric has been investigated as a natural histological stain, with most studies describing predominantly cytoplasmic staining and suggesting turmeric as a replacement for eosin. However, the present study supports the use of turmeric as a counterstain as staining localization is strongly dependent on the solvent, co-solute and procedure used for extraction and for staining. In contrast to several prior reports using alcoholic turmeric extracts, alcohol-based preparations in this study produced little to no appreciable tissue staining despite exhibiting intense coloration in solution. Instead, an aqueous extract with addition of aluminum was the most effective. A 0.5% turmeric solution prepared in aqueous 5% aluminum sulfate produced a bright yellow stain in histologic sections. While yellow chromatin against a colorless background provided limited contrast as a routine nuclear stain substitute, pairing turmeric with selected companion stains yielded favorable results. As a counterstain for alcian blue, Prussian blue, von Kossa, and rhodanine methods, turmeric provided excellent visual contrast. Turmeric is also markedly less expensive than nuclear fast red, supporting its potential as an economical alternative for selected histological applications.