Purple Urine Bag Syndrome: A Rare and Interesting Phenomenon

Noriko Soffi Harun, BMBS, MRCP; Syed Khader Muhammad Shahul Hameed Nainar, MBBS, MD; Vui Heng Chong, MRCP, FAMS


South Med J. 2007;100(10):1048-1050. 

In This Article


PUBS was first reported in 1978.[1] It is rarely encountered, but a prevalence as high as 9.8% has been reported in patients who were in long-term wards.[2] This condition has been commonly reported to occur in the elderly, typically female patient, with a history of constipation, and catheterized with plastic (PVC) urinary catheters.[3] Often these patients have significant comorbidities and are found to have a urinary tract infection.[4] The urine is generally alkaline and this has been reported to be an important factor. Dehydration is also an important factor as the serum concentration of indoxyl sulfate (indican), an important constituent, was found to have a linear correlation with the severity of the azotemia.[5] Both of our patients were female, unwell, dehydrated, constipated, had urinary tract infections and had been catheterized.

Gram-negative bacteria producing sulfatase and phosphatase are important in the pathogenesis.[6,7] Even bacteria of the same species may not cause this syndrome due to the lack of these enzymes. This may explain the rarity of this phenomenon despite the frequent occurrence of urinary tract infections in clinical practice. The presence of constipation promotes bacterial overgrowth and a high bacteria load has been reported to be an important factor. Commonly reported organisms include Providencia species, Klebsiella pneumoniae, E coli, Proteus species, Morganella species, Pseudomonas species and Enterobacter species.[8] It is occasionally difficult to differentiate which organisms are responsible, as isolation of multiple organisms is not uncommon. However, certain organisms have consistently been isolated as the only organism present, and definitely have been shown to be associated with this syndrome. The presence of multiple organisms has been shown to enhance the activities of the enzymes responsible for pigment formation. Bacteria implicated in the pathogenesis of PUBS are listed in the Table 1 .[3,6,7,8,9,10,11,12]

The purple discoloration in the urinary bag and the bluish discoloration of the catheter are due to the presence of indigo (blue) and indirubin (red) in the urine.[5,7,8] Other pigments are also formed, but do not cause discoloration. The pathogenesis of PUBS is shown in Figure 2. The formation of these pigments is related to the metabolism of tryptophan in the intestine. Low serum tryptophan has been shown to occur in patients with PUBS as a result of sequestration within the intestine. A high tryptophan diet may increase the risk of developing this syndrome in susceptible patients. This may account for the reported high incidence in some series where patients' diet may be high in tryptophan.[2,3]

Metabolic pathways of purple urine bag syndrome (+ ve indicate factors that contribute to pathogenesis).

Despite the unusual discoloration that can be alarming, this syndrome only indicates the presence of an underlying urinary tract infection that can be easily treated. Therefore, clinicians need to be aware of this syndrome and initiate treatment for urinary tract infection as soon as possible, as the outcome may be fatal if it progresses to generalized septicemia. This is particularly so as patients reported to develop this condition are often elderly, unwell and have significant comorbid conditions. This was the case in our first patient. Interestingly, purple diaper syndrome has also been reported and the pathogenesis is believed to be the same as that of PUBS.[13]


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