Description

A 75-year-old woman presented reporting of feeling generally unwell. She had a history of cervical cancer, radiation enteritis and chronic urinary tract obstruction managed with a long-term urinary catheter. She was hypovolaemic and her urine was strikingly purple in colour (see figure 1) and malodourous. Urine dipstick was positive for nitrites and leucocytes; inflammatory markers were raised; and subsequent urine culture grew Escherichia coli, Klebsiella pneumoniae and Morganella morganii. She was treated with intravenous antibiotics and fluid resuscitation, her urinary catheter was changed, and the urine returned to a normal colour over 24 h.

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Figure 1

Purple discolouration of the catheter bag in response to urinary tract infection.

Discolouration of the urine may indicate significant pathology, and visual inspection of the urine should form part of routine clinical examination. The purple urinary bag syndrome was first described in 1978 and refers to the rare but potentially alarming phenomenon of the urine and catheter bag turning purple in response to urinary tract infection.1 It usually occurs in elderly patients with long-term urinary catheters. Intestinal bacteria metabolise tryptophan to indole, which is absorbed and conjugated to indoxyl sulfate (IS). IS is excreted in the urine where it may be converted to indigo (blue) and indirubicin (red) by indoxyl sulfatase and phosphatase enzymes. Indigo and indirubicin precipitate on to the catheter and catheter bag together as an intense purple colour.2 The syndrome occurs due to high levels of IS in the urine and the presence of bacteria that are capable of producing these enzymes: E. coli, K. pneumoniae, Providencia stuartii and Providencia rettgeri, Proteus mirabilis, and M. morganii.