Recognizing purple bag syndrome at first look

Caterina Canavese, Andrea Airoldi, Marco Quaglia, Maria Cristina Barbè, Maddalena Brustia, Matteo Vidali, Marco Bagnati, Stefano Andreone, Tjibbo Corrà, Calogera Sciarrabba, Giorgio Bellomo, Piero Stratta

Research output: Contribution to journalArticlepeer-review


Purple urine bag syndrome is a clinical entity first described in 1978. Its typical discoloration is worrying for clinicians. In the past, these patients sometimes reached the emergency unit only because of this exceptional worrying urinary sign and underwent invasive diagnostic examinations including cystoscopy, without any abnormal finding. It is now clear that this astonishing phenomenon of double discoloration of the urine, appearing purple in the bag and dark blue in the test tube, results from the formation of 2 different pigments (indirubin and indigo) in very alkaline urines due to enzymes produced by gram-negative bacteria, such as indoxyl phosphatase/sulfatase, which can convert urinary metabolites of dietary tryptophan. Practicing physicians should identify purple urine bag syndrome as a usually benign medical condition diagnosed in asymptomatic patients, which only requires treatment of bacteriuria with antibiotics, prevention of constipation, substitution of catheter and acidification of the urine. After these measures, urine typically returns to its normal color.

Original languageEnglish
Pages (from-to)465-469
Number of pages5
JournalJournal of Nephrology
Issue number3
Publication statusPublished - May 2013


  • Chronic catheterization
  • Dietary tryptophan
  • Gram-negative urine infection
  • Purple urine

ASJC Scopus subject areas

  • Nephrology


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