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March 22, 2018
Congo Red Stain Tutorial

- Published: March 22, 2018
- By: Chris Larsen, MD
- Tags: Amyloidosis, Congo red, Proteinuria
Positive Congo red staining in tissue with apple-green birefringence under polarized light is diagnostic of the presence of amyloid fibrils. Image A shows a glomerulus with Congo red positive mesangial staining while image B shows a renal biopsy with diabetic nephropathy that is negative for Congo red. Accurate interpretation of this stain hinges upon proper optimization so that there is elimination of nonspecific background staining.