July 5, 2012

Image of the Day 12: Purple Urine Bag Syndrome

This picture belongs to a 46 years old man who presented with Urinary tract infection. Can you see what is wrong with the Urinary bag and the tube's  color. It's purple in color. It did not means that this patient is an alien secreting a weird toxic liquid from his body. This condition is also not associates with any drug given to the patient. This condition is called "Purple Urine Bag Syndrome". It is a very rare condition that first reported in 1978 by Barlow and Dickson.

The condition is associated with female gender, alkaline urine, constipation, institutionalisation and the use of plastic urinary catheter. All these factors with the combination of higher bacterial load in urine facilitates the development of this syndrome. It is often associated with Providencia spp., E. coli, Proteus spp., Pseudomonas spp., Klebsiella pneumoniae, Morganella spp. and Enterococcus spp. Less commonly reported associations include Citrobacter spp., Staphylococcus spp., Streptococcus spp. and even MRSA (Pillai B P et al)

The theory behind this syndrome is due to the metabolism of tryptophan by the gut bacteria into indole. The indole is then converted to the indoxyl sulphate (or indican) in the liver and excreate into the urine. Bacteria that possess and an enzyme (phosphatase with minor sulfatase activity) will then act on the indoxyl sulphate to produce indigo. The purple discoloration of the urine bag occurs as a result of indirubin (which is red) dissolving in the plastic and mixing with the fine blue indigo crystals in the urine. [Mylene B. Vicuna et al]

Some literature point a different hypothesize for example by Barlow and Dickson who propose that indoxyl sulfate is oxidized to indigo only after urinary excretion and exposure to air. Sammons et al theorized that indicanuria in patients leads to a blue color only when the urine is treated with an oxidizing agent such as sodium hypochlorite (bleaching powder) [Mylene B. Vicuna et al]

In another observation, purple discoloration of the urine was associated with a highly alkaline urine in contact with the plastic collecting bag, which caused the dye used to eliminate the yellow tint of the bag to discolor the urine [Mylene B. Vicuna et al]. However, this syndrome also occurs in acidic urine.

Study using mass spectroscopy suggested that the molecular structure of the causative pigment is a steroidal or bile acid conjugate, not indigo. [Mylene B. Vicuna et al]

This problem is managed with antibiotic and does not require aggressive treatment. apart from that, it is important to advocate constipation control and urological sanitation. The parent and relative should be educated regarding this problem and inform them that it is not dangerous.


1. Mylene B. Vicuna, Pia S. Lorenzo & Sajan Thomas, "Purple Urine Bag Syndrome in an
Elderly Nursing Home Resident", Hospital Physician May 2007.

2. Pillai B P, Chong V H, Yong A M L, "Purple urine bag syndrome", Singapore Med J C a s e R e p o r t 2009; 50(5) : e193.

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