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Purple urinary bag syndrome

About the author

I am Katie and I live in Cornwall. As a result of nerve damage following a sacral fracture, I had surgery to create a urostomy in 2003, and in 2008 I had further surgery, this time to create a colostomy.

Until I retired, I was an Associate Lecturer in Health and Social Care with the Open University doing quite a bit of research work as well as teaching the students, many of whom were nurses. I absolutely love doing research and, following several messages on the UA Facebook group page about urine suddenly turning purple (which can be scary!), I decided to investigate this phenomenon.

So, what is purple urinary bag syndrome?

If you wake up one morning and find that the urine in your catheter or night drainage bag has suddenly turned purple it can be very alarming.

So…we thought it would be a good idea just to outline what Purple Urinary Bag Syndrome (PUBS) is and what it may mean if your urine bag suddenly becomes purple overnight.

PUBS was first reported in the medical literature in 1978. It is an uncommon (some say rare) condition occurring in people who may be catheterised or who have other forms of urinary diversions where the urine is drained into a drainage bag.

Why does the urine appear to turn purple?

The purple colouration is the result of the breakdown, through the digestive system, of a building block of protein called tryptophan (found in a range of foods including milk, fish, chicken and turkey). In certain situations, a resultant by-product of the metabolism of tryptophan – indoxyl sulphate – reacts with bacteria in the urine to produce two pigments indigo (blue) and indirubin (red). We know from our childhood paint box that red and blue combine to make purple. Hence the purple colour!

Interestingly it is not the urine itself that is purple. The bag or catheter turns purple when increased levels of these pigments react with the plastic to produce the purple discolouration.

Why does it only happen sometimes and to just some people?

In the medical literature a number of risk factors for this syndrome have been identified, which may include:

  • A urinary tract infection, where there may, or may not, be any urinary tract infection (UTI) symptoms – PUBS does not seem to be associated with any particular bacteria. In their paper “Purple Urine Bag Syndrome: More Than Eyes Can See” the authors identify over 20 different bacteria which have been associated with UTIs relating to PUBS, including E.Coli, Proteus Mirabilis and Pseudomonas aeruginosa.
  • An alkaline urine (although there have been a few reports of PUBS where urine is acidic)
  • Constipation
  • Catheterisation or other urinary diversion
  • Use of a polyvinyl chloride urinary catheter or bag

Treating and preventing PUBS

PUBS is usually associated with a UTI so the steps that can be taken when it is seen include:

  • Deciding whether to treat any underlying UTI with antibiotic
  • Treating the constipation
  • Maintaining good personal hygiene
  • If an indwelling catheter is present, change it regularly
  • If urinary drainage bags are used, change them regularly

Important to remember:

If you suddenly wake up and see purple urine…Don’t panic!! It is not, in itself, a serious condition but it can point to an underlying UTI. So do make sure you seek medical advice to ensure you can get the correct treatment.


“Purple Urine Bag Syndrome: More Than Eyes Can See” Sabanis N, Paschou E, Papanikolaou P and Zagkotsis Department of Nephrology; Department of General Practice & Family Medicine, General Hospital of Livadeia, Voiotia, Greece in Current Urology 2019: 125-132

“Urine Bags Syndrome masquerading as a bowel obstruction” Declan McDonnell 2019 Conquest Hospital, St Leonards-on-Sea, East Sussex, UK (

“Purple Urine Bag Syndrome: A Rare Spot Diagnosis” Dilraj S. Kalsi, Joel Ward, Regent Lee, and Ashok Handa Published online Dis Markers 29 Nov 2017 ( )

Katie M Sainsbury BSc (Edin) BA (Open)

  • Katie’s findings were published in our own Urostomy Association Journal in 2021 and in Tidings (Colostomy UK’s Journal ) in 2023.