Purple Urine Bag Syndrome (PUBS)
Overview
PUBS is a visually striking phenomenon seen mainly in older, chronically catheterised patients.
Purple discolouration of urine and catheter tubing/bags results from bacterial pigment production and usually indicates catheter colonisation; it may-but does not always-reflect clinically significant catheter‑associated urinary tract infection (CAUTI).
In the emergency department (ED) PUBS should prompt targeted clinical assessment, appropriate specimen collection when indicated, catheter review, and adherence to guideline‑based antibiotic stewardship (NICE NG113; QS90).
Pathophysiology (concise)
- Dietary tryptophan is converted by gut bacteria into indole.
- Indole is metabolised in the liver to indoxyl sulphate and excreted in urine.
- Certain urinary bacteria (via indoxyl sulphatase/phosphatase) convert indoxyl sulphate to indigo (blue) and indirubin (red) pigments.
- The mixture of indigo and indirubin produces the characteristic purple colour in urine and drainage systems.
- Alkaline urine, bacterial overgrowth (favoured by constipation), and chronic catheterisation promote pigment production and visible discolouration.
Epidemiology and risk factors PUBS is most often seen in:
- Older, frail patients, with a female predominance.
- Patients with long‑term indwelling urinary catheters (urethral or suprapubic).
- Patients with constipation or decreased gut motility.