Purple urine bag syndrome

Purple urine bag syndrome (PUBS) can occur in the tubing and urine bag.

PUBS results from a bacteriuria or infection with a gram negative bacteria and tryptophan from the diet with red and blue pigments causes a purple colour to the urine.

Risks for development of PUBS include:

• 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

Gram-negative bacteria produce indoxyl phosphatase or sulphatase, an enzyme that converts indoxyl sulphate (a tryptophan metabolite) for indirubin (coloured red) and indigo (coloured blue). These two substances, when mixed, produce purple colouration of the urine.