Purple urine bag syndrome
Purple urine bag syndrome (PUBS) results from a combination of bacteriuria or infection with a gram-negative bacteria and tryptophan, from the diet, with red and blue pigments turning the urine to a purple colour. Purple urine bag syndrome (PUBS) can occur in the tubing and urine bag.
Risks for the development of PUBS:
The following factors can increase the risk of a person with SCI, using a catheter, developing PUBS:
- Long-term use of indwelling catheters
- Increased tryptophan in diet – meat, fish (salmon, canned tuna), soybeans (including tofu and cow’s milk)
- Constipation
- Renal failure
- High bacterial load in the urine
What is gram-negative bacteria?
Gram-negative bacteria produce indoxyl phosphatase or sulphatase, an enzyme that converts indoxyl sulphate (a tryptophan metabolite) to indirubin (coloured red) and indigo (coloured blue). These two substances, when mixed, produce purple colouration of the urine.
Examples of gram-negative bacteria include:
- Klebsiella
- Pseudomonas
- Escherichia coli
- Proteus
- Providencia
- Morganella
- Citrobacter
- Enterococci
- Group B Streptococci

Purple Urine Bag image sourced from Purple Urine Bag – Craig Hospital
Ansari, A., Azim, T & Srinivasan, V. (2021) Purple urine bag syndrome. Urology News Vol.25 No 5. Purple urine bag syndrome | Urology News
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