Shades of Purpleness

Unusual Urine 005

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

Purple Urine

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)
  • Bacteria such as Providencia stuartii, Klebsiella pneumoniae, P. aeruginosa, Escherichia coli, and enterococcus species are most commonly implicated
  • The clinical course is benign, and the urine typically clears with resolution of the bacteriuria and acidification of the urine.

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