Key Takeaways
Urine colour can provide important diagnostic information. For example, orange urine may indicate a urinary tract infection (UTI), liver disease, or bile duct disorder. Dr Marco Franzoi and colleagues from the Department of Internal Medicine at Hospital of the Brothers of Mercy in St. Veit an der Glan, Austria, reported a rare case of purple urine in a patient.
The authors used this case to explain the causes and clinical significance of the purple urine bag syndrome (PUBS).
The Patient and Her History
An older woman with dementia presented to the emergency department with fever and worsening of her overall condition. She had an indwelling urinary catheter, and her urine was purple in colour (approximately 250-300 mL).
Findings and Diagnosis
The findings were as follows:
- No open wounds or diarrhoea.
- Palpable resistance in the lower abdomen corresponding to urinary retention with a distended bladder, as confirmed by ultrasound.
- Correct positioning of the catheter balloon in the bladder.
- Replacement of the indwelling catheter, but purple urine persisted, followed by pyuria.
- Laboratory tests revealed moderate leucocytosis and an elevated C-reactive protein level of 27 mg/dL.
- The renal function and electrolyte balance were normal.
- Urine tests identified bacterial growth and confirmed the presence of Proteus mirabilis, which was susceptible to ceftriaxone on the basis of antimicrobial susceptibility testing.
The patient was treated with antibiotics according to the test results, recovered without complications, and was subsequently discharged from the nursing home.
Discussion
Urine has been a key diagnostic tool since ancient times.
Hippocrates was considered the first urologist until the Victorian era, when urine was used as a primary diagnostic tool. Colour, odour, sediment, and taste are used to identify diseases. During the seventh century, the physician Theophilus Protospatharius presented the manuscript “De Urinis,” which was the first publication exclusively on the subject of urine. The book describes several urine discolourations and their clinical correlations. In the 12th century, Gilles de Corbeil introduced the matula, a glass vessel designed to assess the colour and clarity of urine under direct sunlight.
As the authors emphasised, the importance of urine colour can indicate a range of conditions. For instance, transparent or pale-yellow urine suggests good hydration, while amber urine shows dehydration. Distinct urine colours may indicate underlying diseases. For instance, orange urine may indicate dehydration, UTIs, liver or bile duct disorders, or the use of certain medications. Red urine, often linked to haematuria, can also result from benign causes (eg, beetroot consumption) or serious conditions (eg, infections, nephrolithiasis, and malignancies).
First described in The Lancet in 1978, PUBS is a rare condition that causes purple urine in patients with bacterial infection. The discolouration results from disrupted tryptophan metabolism. Tryptophan is converted into indole by gut bacteria, which enters the bloodstream and is transported to the liver. The authors explained that the enzyme CYP2E1 metabolises indole into 3-hydroxyindole, which is sulphonated into indoxyl sulphate and excreted via the kidneys.
In alkaline urine, indoxyl sulphate oxidises into indigo (blue) and indirubin (red), which interact with the catheter’s plastic, causing purple discolouration that deepens over time.
In patients with indwelling catheters, gram-negative bacteria such as P mirabilis, Escherichia coli, and Klebsiella pneumoniae break down indoxyl sulphate, further contributing to this discolouration.
While PUBS is associated with bacterial colonisation of the urinary tract, treatment depends on the presence of clinical symptoms of a UTI, such as fever, dysuria, or flank pain. Antibiotic treatment is initiated when such symptoms are present. In the absence of typical symptoms, antibiotics are not recommended, except in certain cases, such as during pregnancy.
Several factors increase the risk of developing PUBS, including female sex, advanced age, constipation, institutionalisation, long-term catheterisation, chronic kidney disease, alkaline urine, and high bacterial counts in the urine. However, PUBS is not exclusive to patients with indwelling catheters. Reports have linked this syndrome to chronic constipation and the use of laxatives.
This article was translated from Univadis Germany using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.