Indoxyl sulfate, also known as 3-indoxylsulfate and 3-indoxylsulfuric acid, is a metabolite of dietary l-tryptophan that acts as a cardiotoxin and uremic toxin. High concentrations of indoxyl sulfate in blood plasma are known to be associated with the development and progression of chronic kidney disease and vascular disease in humans. As a uremic toxin, it stimulates glomerular sclerosis and renal interstitial fibrosis.