purple urine bag syndrome

A 78-year-old male is brought in from his nursing home for evaluation of hypotension. He has a prior history of multiple strokes and is bed bound. He arrives febrile, tachycardic, and hypotensive. On your physical exam, you notice that he has an indwelling foley catheter. The catheter tubing and bag have a vibrant purple color. You wonder if this unusual urine color could be caused by something insidious. Could this be related to a toxin, medication, or infection?

What is Purple Urine Bag Syndrome?

Purple Urine Bag Syndrome (PUBS) is an uncommon presentation in patients with indwelling foley catheters. It is most frequently caused by an underlying urinary tract infection [1,2]. The urine is actually a dark brown color, but interaction with the plastic bag and tubing turns them into a bright purple [3]. The discoloration of the bag denotes the presence of an infection, but by itself is generally a benign process. However, as in this case, the presence of PUBS may indicate a urinary source for sepsis. Cases are increasing since initially described in 1978 and is thought to be from an increasing elderly population [1].

What are risk factors for PUBS? [1]

  • Elderly population
  • Poor hygiene of indwelling foley catheter
  • Female sex
  • Chronic constipation
  • Recurrent UTI
  • Institutionalization
  • Dementia
  • Chronic kidney disease
Purple urine bag pathogenesis (Interntl J of Gen Med)

How does the urine bag become purple?

The purple hue is caused by the metabolism of tryptophan. It is thought that constipation and delayed gut motility can lead to bacterial overgrowth. The bacteria then break down tryptophan into indole. Indole is then converted to indoxyl sulfate by CYP enzymes in the liver. Once in an alkalinized urine environment, bacteria that have sulphatase and phosphatase enzymes convert indoxyl sulfate into indigo and indirubin. The blue color of indigo and the red of indirubin combine and react with the plastic tubing to turn the tubing and collection bag purple [1].

Occasionally, this occurs in the absence of infection and is caused by passage of bile acids in the urine [1]. 

What Bacteria Cause PUBS?

The bacteria are primarily gram negative and contain the needed sulphatase and phosphatase enzymes [1,2]. 

  • Escherechia coli (most common bacteria associated with PUBS). 
  • Klebsiella pneumoniae
  • Proteus species
  • Morganella morganii
  • Enterococcus species
  • Pseudomonas species

Why does this matter?

PUBS is usually a benign process, but if left untreated could lead to more profound infection [3]. Recognizing this diagnosis can lead to prompt antibiotic therapy against primarily gram negative organisms. It also lends itself to mitigating the underlying risk factors in these patients, such as more frequent catheter exchanges, bowel regimens, and improved care for the geriatric population. 


  1. Sabanis N, Paschou E, Papanikolaou P, Zagkotsis G. Purple Urine Bag Syndrome: More Than Eyes Can See. Curr Urol. 2019;13(3):125-132. doi:10.1159/000499281
  2. Al Montasir A, Al Mustaque A. Purple urine bag syndrome. J Family Med Prim Care. 2013;2(1):104-105. doi:10.4103/2249-4863.109970
  3. Mohamad Z, Chong VH. Purple urine bag: think of urinary tract infection. Am J Emerg Med. 2013;31(1):. doi:10.1016/j.ajem.2012.04.010
  4. Vallejo-Manzur F, Mireles-Cabodevila E, Varon J. Purple urine bag syndrome. Am J Emerg Med. 2005;23(4):521-524. doi:10.1016/j.ajem.2004.10.006
Robert Barnes, MD

Robert Barnes, MD

Assistant Professor
Assistant Program Director
Department of Emergency Medicine
UT Southwestern Medical Center
Robert Barnes, MD

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Justin Hornbeck, MD

Emergency Medicine resident
UT Southwestern Medical Center

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