What is Purple Syndrome? Understanding Purple Urine Bag Syndrome (PUBS)

September 28, 2025 •

5 min read

Affecting nearly 10% of institutionalized patients with long-term urinary catheters, purple urine bag syndrome (PUBS), colloquially known as purple syndrome, is a visually startling but typically benign medical phenomenon. It arises from a specific bacterial-chemical reaction in the urine drainage system, causing the tubing and bag to turn a vibrant purple color.

Quick Summary

Purple urine bag syndrome (PUBS) is a rare condition where bacteria in the urine, interacting with a breakdown product of tryptophan and the plastic of a urinary catheter and bag, cause the drainage system to turn purple. It is often associated with long-term catheterization and chronic constipation, typically indicating an underlying urinary tract infection.

Key Points

What is purple syndrome?: It is the common name for Purple Urine Bag Syndrome (PUBS), a condition where a patient's catheter and bag turn purple due to a specific bacterial-chemical reaction in the urine.
What causes it?: The discoloration occurs when certain bacteria, present in an underlying urinary tract infection, react with a breakdown product of tryptophan in the urine.
Who is at risk?: Elderly, bedridden, and institutionalized patients with long-term urinary catheters and chronic constipation are most susceptible.
Is it dangerous?: The purple discoloration itself is generally harmless, but it indicates an underlying urinary tract infection that requires medical attention.
How is it managed?: Management involves replacing the catheter and bag, treating any symptomatic UTI with antibiotics, and addressing associated risk factors like constipation.
How can it be prevented?: Key preventive measures include proper catheter hygiene, addressing constipation, ensuring good hydration, and regular catheter changes.

What is Purple Urine Bag Syndrome (PUBS)?

Purple Urine Bag Syndrome (PUBS) is a rare medical condition characterized by a striking purple or blue discoloration of a patient's urinary catheter bag and tubing. While alarming to see, the phenomenon is caused by a chemical reaction involving certain bacteria and a metabolic byproduct in the urine. First described in 1978, PUBS is most commonly observed in elderly, chronically debilitated, and institutionalized patients who have indwelling urinary catheters for long periods. While it signals an underlying urinary tract infection (UTI), the condition itself is often asymptomatic and benign. However, recognizing its presence is crucial, as it indicates a need to address the underlying infection and related risk factors.

The Biochemical Pathway Behind the Purple Hue

The vibrant purple color is the result of a fascinating biochemical process involving the amino acid tryptophan, a component of many foods.

Tryptophan Metabolism: In the gastrointestinal tract, bacteria break down undigested tryptophan into a compound called indole.
Indole Conversion: The liver then converts this indole into indoxyl sulfate.
Urinary Excretion: Indoxyl sulfate, also known as indican, is then excreted in the urine.
Bacterial Reaction in the Catheter: If an indwelling catheter is present and the urine is alkaline, specific bacteria—such as Providencia stuartii, Proteus mirabilis, Klebsiella pneumoniae, and Escherichia coli—that carry sulfatase and phosphatase enzymes will act on the indoxyl sulfate.
Pigment Formation: This enzymatic reaction oxidizes the indoxyl sulfate into two pigments: indigo (blue) and indirubin (red).
Purple Discoloration: The mixture of these blue and red pigments adheres to the plastic material of the catheter and bag, resulting in the deep purple coloration. The final shade of purple depends on the relative concentration of the two pigments.

Key Risk Factors for Developing PUBS

PUBS is not a random occurrence; several factors significantly increase a patient's risk of developing the condition:

Long-Term Catheterization: Extended use of an indwelling urinary catheter is the most critical risk factor, providing the necessary environment for the bacterial-chemical reaction to occur.
Chronic Constipation: Constipation slows bowel motility, increasing the time tryptophan metabolites remain in the gut and leading to higher levels of indoxyl sulfate in the urine.
Alkaline Urine: An alkaline urinary environment is necessary for the bacterial enzymes to break down the indoxyl sulfate into the color-forming pigments. This can result from the underlying UTI or other health issues.
Female Gender: The condition is more frequently reported in elderly women, possibly due to a higher prevalence of urinary tract infections in this demographic.
Institutionalization and Immobility: Elderly or chronically debilitated patients in nursing homes or long-term care facilities are at higher risk. Immobility contributes to constipation and other complications.
Comorbidities: Patients with conditions like dementia, chronic kidney disease, or spinal cord injury are also at an increased risk.

Signs and Symptoms

The most obvious sign of PUBS is the unmistakable purple, blue, or reddish discoloration of the catheter bag and tubing. However, it is important to note that the urine itself, when freshly voided, may appear normal. Caregivers may also observe:

Strong, Foul Odor: The underlying UTI often causes the urine to have a very strong odor.
Cloudy Urine: The urine may appear cloudy due to the presence of bacteria and pus cells.
Signs of UTI: While often asymptomatic, some patients may exhibit symptoms of a standard UTI, such as fever, chills, fatigue, or confusion, especially in elderly patients.

Diagnosis and Management

Diagnosis of PUBS is often made visually based on the characteristic discoloration. The underlying cause—the urinary tract infection—is confirmed through urine culture and analysis.

Management focuses on addressing the root causes and includes several steps:

Catheter Replacement: The most immediate action is to replace the old, discolored catheter and bag, as the discoloration is confined to the plastic surfaces.
Addressing the Underlying UTI: Antibiotics may be prescribed if the patient is symptomatic or if a high bacterial load is found in the urine culture. However, antibiotic use is not always necessary for asymptomatic cases.
Treating Constipation: Ensuring regular bowel movements is vital. This may involve increasing dietary fiber, ensuring adequate hydration, and using laxatives if necessary.
Improving Hygiene: Good catheter care practices and proper sanitation can help reduce the frequency of UTIs and thus lower the risk of recurrence.
Addressing Comorbidities: Managing chronic conditions like kidney disease or dementia is part of a comprehensive care plan.

Comparison of PUBS with Other Causes of Colored Urine

It is important to distinguish PUBS from other conditions that can cause unusual urine coloration. The table below provides a helpful comparison.


Condition	Cause	Urine Color	Catheter/Bag Discoloration?
Purple Urine Bag Syndrome (PUBS)	Bacterial enzymes act on tryptophan metabolite (indoxyl sulfate) in the urine.	Can appear normal or slightly discolored.	Yes, the bag and tubing turn purple.
Hematuria (blood in urine)	Bleeding in the urinary tract from infection, injury, or other conditions.	Pink, red, or cola-colored.	No
Alkaptonuria (genetic disorder)	Lack of an enzyme leads to homogentisic acid buildup.	Initially normal, darkens to brown or black on exposure to air.	No
Medications (e.g., phenazopyridine)	Various drugs can alter urine color as a side effect.	Can be orange, red, or blue-green, depending on the medication.	No
Diet (e.g., eating beets)	Pigments from certain foods can temporarily change urine color.	Red or pink.	No

Prognosis and Prevention

In most cases, PUBS is a benign and easily manageable condition with a good prognosis. The purple discoloration often resolves within days of catheter replacement and treatment of the underlying infection and risk factors. However, ignoring the signs can lead to more serious complications from an untreated UTI, particularly in vulnerable patients.

Preventing PUBS largely involves good catheter management and addressing the associated risk factors. Regular catheter changes, maintaining excellent hygiene, ensuring proper hydration, and managing chronic constipation are key preventive strategies. For example, studies have found that better catheter care can significantly reduce the occurrence of PUBS. Raising awareness among caregivers, family members, and healthcare staff is also vital, as the unusual appearance can cause unnecessary alarm. Education helps ensure prompt and appropriate management, rather than aggressive and potentially unnecessary antibiotic treatment. A good resource for understanding PUBS is provided by the Journal of Pain and Symptom Management.

Conclusion

Purple syndrome, or Purple Urine Bag Syndrome, is a distinct clinical sign resulting from the metabolic breakdown of tryptophan by bacteria in the context of an indwelling urinary catheter and alkaline urine. While its appearance can be startling, it is usually a benign indicator of an underlying urinary tract infection in susceptible patients, such as the elderly with chronic constipation. Proper management focuses on addressing the root causes, including catheter changes, treating the infection if symptomatic, and managing constipation. With timely intervention and proper care, PUBS is a temporary and treatable condition, though it serves as a critical visual cue for caregivers to investigate a patient's overall health status.

Frequently Asked Questions

Purple Urine Bag Syndrome, or PUBS, is a condition where the plastic catheter tubing and collection bag turn purple or blue. It happens in patients with long-term urinary catheters due to a chemical reaction triggered by an underlying urinary tract infection and other factors like chronic constipation.

The urine itself may or may not be purple. The chemical reaction often causes the pigments (indigo and indirubin) to adhere predominantly to the plastic material of the bag and tubing, rather than remaining dissolved in the urine.

The bacteria most commonly involved are gram-negative bacteria, including Proteus mirabilis, Escherichia coli, Pseudomonas aeruginosa, and Providencia stuartii. These bacteria produce enzymes that contribute to the chemical reaction.

Not necessarily. If the patient is asymptomatic (has no symptoms like fever or pain), antibiotics may not be needed. Treatment often focuses on replacing the catheter and addressing risk factors like constipation. However, if a symptomatic UTI is present, antibiotics may be required.

Caregivers can help prevent PUBS by ensuring proper catheter hygiene, regularly changing the catheter and bag, encouraging adequate fluid intake, and managing constipation. Awareness of the condition can also prevent unnecessary panic among family members.

While PURPLE crying is a term used for a developmental phase in infants, Purple Urine Bag Syndrome (PUBS) is primarily associated with long-term urinary catheterization and is most common in elderly or chronically debilitated individuals, not infants. The two are unrelated.

If you notice a purple urine bag, you should contact a healthcare professional. They will assess the patient to determine if there are any signs of a symptomatic infection and create a management plan, which usually includes changing the catheter and addressing any underlying issues.