Purple Urine Bag Syndrome — SCE Infectious Diseases MCQ

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EasyHealthcare-Associated InfectionsPurple Urine Bag SyndromeSCE Infectious Diseases

A 65-year-old man with a long-term urinary catheter develops purple discolouration of the urine collection bag and tubing. He has chronic constipation and is otherwise well. Urine culture grows mixed organisms including Providencia stuartii. What is this phenomenon?

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Correct answer: A — Purple urine bag syndrome (PUBS)

PUBS is a striking but benign condition caused by bacterial enzymes (produced by Providencia, Klebsiella, Proteus, E. coli, Pseudomonas) metabolising dietary tryptophan in the gut to indole, which is absorbed, conjugated in the liver to indoxyl sulphate, and excreted in urine. Urinary bacteria then convert indoxyl sulphate to indigo (blue) and indirubin (red), which combine to produce a purple colour that stains the plastic catheter bag. Risk factors include chronic catheterisation, constipation (increases tryptophan gut metabolism), and alkaline urine. Treatment is catheter change and addressing constipation. Antibiotics are not required unless there is clinical infection.

Reference: https://www.nice.org.uk/guidance/conditions-and-diseases/infections