Shades of Purpleness

Unusual Urine 005

Purple Urine

A 76-year-old male nursing home resident with dementia and end-stage renal disease who was undergoing hemodialysis was admitted to the hospital after a syncopal episode that occurred during dialysis. When a urinary catheter was placed, purple urine was drained. The urinalysis showed a pH of 9.0 and bacteriuria but no hematuria or pyuria – NEJM Clinical Case

What is the biochemical cause of purple urine?

Urine can present in a veritable rainbow of colours

Purple discoloration can occur in alkaline urine as a result of the degradation of indoxyl sulfate (indican), a metabolite of dietary tryptophan, into indigo (which is blue) and indirubin (which is red) by bacteria such as Providencia stuartii, Klebsiella pneumoniae, P. aeruginosa, Escherichia coli, and enterococcus species.

The clinical course is benign, and the urine typically clears with resolution of the bacteriuria and acidification of the urine.

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