Updated 27 November 2019

This rare condition turns your pee purple

What could possibly cause your pee to turn a vivid shade of purple?

A recently published case report in the New England Journal of Medicine focused on a rare chemical reaction on the body that can transform your normally slightly yellow urine into a vivid shade of lilac.

According to the report, a 70-year-old woman was hospitalised after having a stroke. Ten days after being admitted, doctors noticed that the urine in her catheter was a bright shade of lilac.  

Usually, a drastic change in the appearance of the urine would be immediate cause for alarm as it can signal severe dehydration or kidney damage. But in this case, it was simply a rare, harmless chemical reaction also known as “purple urinary bag syndrome” (PUBS). This phenomenon was first recorded in medical literature in 1978 and appears on the odd occasion, according to the Annals of Long-term Care.

How does urine turn purple?

Experts explain that PUBS occurs because of a reaction between bacteria and the amino acid tryptophan. According to a research paper in the Journal of Family Medicine and Primary Care, PUBS is often associated with the following factors: female gender, alkaline urine, constipation, a prolonged hospital stay, the inability to move and the use of a plastic catheter and bag.

The higher bacterial load in urine, combined with the above factors, causes the urine to turn bright lilac. The lilac colour is derived from the metabolites of tryptophan as the protein is metabolised in the gastrointestinal tract by gut bacteria.

In the latest case, the doctors found bacteria called Klebsiella pneumoniae, normally found in the human gut and able to cause infection throughout the body, reported Live Science. A diet rich in tryptophan (found in foods like turkey, red meat and dairy) can offset a reaction in the gut, where tryptophan interacts with the higher bacteria count in the urine and breaks down to a chemical called indoxyl sulfate, which ultimately turns the pee purple.

Is it serious?

According to an article in the Canadian Urological Association Journal, purple pee might signal an underlying condition such as a urinary tract infection. Besides the discovery of the bacteria in her urine, the woman had no underlying infection and the pee turned back to its normal yellow hue after she received hydration through an intravenous drip.

Should my pee be that colour?

Urine often varies in shades, depending on your hydration levels – a light shade of lemonade indicates proper hydration, while dark yellow or orange signifies dehydration.

There are, however, other factors that can discolour your urine such as certain foods or medication. Eating beetroot can turn your pee a pinkish red shade, while some medication can darken the urine significantly. In these cases, the discolouration isn’t dangerous.

Blood in the urine can signify kidney or urinary tract infections, while dark urine can be a sign of a problematic liver. See your doctor if the problem persists and if the weird shade of your urine can’t be linked to a food or medicine.

Image credit: iStock, Unsplash


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Dr Prenevin Govender completed his MBChB at the University of Cape Town in 2001. He obtained his Fellowship of the College of Urologists in 2009 and graduated with distinction for a Masters in Medicine from the University of Cape Town in 2010. His special interests include laparoscopic, pelvic organ prolapse and urinary incontinence surgery. He consults full-time at Life Kingsbury Hospital in Claremont.

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