The isolation and identification of indigoid pigments from urine

A purple pigment, phyriaviolin, and a blue pigment, phyriaazulin, have been found in relatively large amounts in the urine of patients suffering from two diverse pathological conditions, porphyria cutanea tarda and Crohn's disease. The two pigments have been characterised by chemical, spectroscopic, and chromatographic studies and identified to be indirubin and indigo (indigotin). Possible reasons for their formation are discussed.