Sudan Red Stain

Sudan red is a lipid-soluble dye used to demonstrate neutral fats and lipid droplets. It stains triglycerides and other lipids red-orange in frozen tissue sections, cell preparations, and stool samples (helpful for detecting steatorrhea). The bright red-orange color highlights adipocytes and intracellular/extracellular fat deposits. It’s also employed in screening for illegal dye contamination in some food products.

A positive Sudan stain indicates excess fat in a stool sample—visible fat droplets or lipid-stained material—consistent with steatorrhea. It suggests fat malabsorption from causes such as pancreatic insufficiency, bile salt deficiency, celiac disease, small-bowel bacterial overgrowth, or short bowel. It's a screening test; further evaluation (quantitative fecal fat, pancreatic function tests, celiac serology, imaging) is usually recommended.

A positive Sudan red test means red-orange fat droplets are seen when a stool sample is stained and examined, indicating excess unabsorbed fat (steatorrhea). It suggests fat malabsorption due to causes such as pancreatic insufficiency, bile salt deficiency, or small‑bowel disease. The result is not diagnostic alone and usually prompts further evaluation (quantitative fecal fat, pancreatic tests, imaging, or celiac workup).

Sudan Red is an industrial azo dye used to color nonpolar materials such as oils, waxes, plastics, solvents and fuels, and sometimes textiles and paints. It’s also used in laboratories as a lipid stain. It has no approved food uses and has been illegally added to spices or processed foods; it’s considered potentially carcinogenic and is restricted or banned for food contact.

Sudan stains are fat-soluble dyes used to detect and visualize lipids in tissues, cells and stool. They’re used in histology (on frozen sections) to highlight neutral fats for diagnosing steatosis or fat emboli, in stool tests for steatorrhea, and in hematology to identify lipid-containing cells (eg, myeloid granules) in clinical and research settings.

The Sudan test for lipids is based on the solubility of lipophilic Sudan dyes in fats: the dye partitions into the lipid phase, staining neutral fats and triglycerides (e.g., red or black droplets) against the aqueous background, enabling qualitative detection of lipids. Non‑lipid components remain unstained. Different Sudan dyes vary in sensitivity, and emulsifiers can interfere with results.