Purple urine bag syndrome

Overview

Purple Urine Bag Syndrome (PUBS) is a rare but striking clinical condition in which the urine in a catheter collection bag turns a deep purple or violet color. Despite its alarming appearance, PUBS is typically benign and often indicates an underlying urinary tract infection (UTI), especially in elderly or chronically catheterized patients. The condition is caused by a chemical reaction involving bacterial enzymes and urinary metabolites. PUBS is most often seen in patients with long-term indwelling urinary catheters, particularly in those who are bedridden or institutionalized.

Although the syndrome is usually harmless, it can be a sign of an ongoing or recurrent UTI, and its presence should prompt clinical evaluation to rule out more serious complications.

Causes

Purple Urine Bag Syndrome occurs due to the breakdown of tryptophan (an amino acid) in the gastrointestinal tract and a series of chemical reactions that lead to the formation of pigments in the urine. The main contributing factors include:

Metabolic Pathway

• Tryptophan is metabolized by intestinal bacteria into indole

• Indole is absorbed and converted to indoxyl sulfate in the liver

• Indoxyl sulfate is excreted in the urine

• Bacteria in the urinary tract with indoxyl sulfatase and phosphatase activity (e.g., Proteus, Pseudomonas, Klebsiella, Providencia, Escherichia coli) convert indoxyl sulfate to indigo (blue pigment) and indirubin (red pigment)

• These pigments mix and bind to the catheter tubing or collection bag, producing the characteristic purple color

Risk Factors

• Female gender (due to shorter urethra and higher UTI risk)

• Chronic urinary catheterization

• Alkaline urine pH

• Constipation (prolongs bowel transit and increases indole production)

• Institutionalization or long-term care residency

• Immobility and poor hygiene

• Advanced age and comorbidities such as dementia or chronic kidney disease

Symptoms

The hallmark symptom of Purple Urine Bag Syndrome is the discoloration of urine to a purple or violet hue. Other symptoms are usually related to the underlying urinary tract infection or associated conditions.

Urinary and General Symptoms

• Purplish discoloration of the catheter tubing and urine collection bag

• Cloudy or foul-smelling urine

• Dysuria or discomfort (rare in patients with indwelling catheters)

• Fever or chills (if associated with systemic infection)

• Confusion or altered mental status in elderly patients

In many cases, the patient remains asymptomatic and the color change is noticed incidentally by caregivers or healthcare providers.

Diagnosis

Diagnosis of Purple Urine Bag Syndrome is clinical and based on the visual appearance of the urine and catheter bag, along with laboratory testing to confirm urinary tract infection and rule out other conditions.

Clinical Evaluation

• Visual inspection of urine and catheter tubing

• Review of medical history and catheter duration

Laboratory Tests

• Urinalysis: May show pyuria, bacteriuria, and alkaline pH

• Urine culture: Identifies causative bacterial organism(s)

• Blood tests: If systemic infection is suspected (e.g., CBC, CRP, blood cultures)

Differential Diagnosis

• Hematuria (red or brown urine)

• Medication-related urine discoloration (e.g., rifampin, amitriptyline)

• Metabolic disorders (e.g., porphyria)

Treatment

Treatment of PUBS focuses on addressing the underlying urinary tract infection, optimizing catheter hygiene, and managing predisposing factors. In most cases, the discoloration resolves once the infection is treated and the urinary tract is cleared of bacteria.

Medical Management

• Antibiotics: Prescribed based on urine culture sensitivity results; empirical therapy may start with broad-spectrum antibiotics

Catheter Care

• Catheter replacement: Removal and replacement of the existing catheter and bag can help clear the discoloration

• Improved catheter hygiene: Regular cleaning and maintenance reduce the risk of infection

Addressing Risk Factors

• Treat constipation: Laxatives or dietary changes to reduce indole production in the gut

• Ensure adequate hydration: Helps flush the urinary tract and reduce bacterial colonization

• Acidify the urine: In some cases, changing the urine pH may discourage bacterial enzyme activity (though this is not routinely done)

Prognosis

Purple Urine Bag Syndrome is generally a benign condition and resolves with appropriate antibiotic therapy and catheter management. The discoloration itself does not indicate severity but serves as a visual marker for underlying infection or poor catheter hygiene.

While the prognosis is favorable in most cases, delayed recognition or treatment of associated urinary tract infections, especially in frail, elderly, or immunocompromised patients, can lead to complications such as urosepsis or worsening renal function. Therefore, early identification and treatment are important to avoid progression.

Preventive measures such as regular catheter care, managing constipation, and avoiding prolonged catheter use when possible can significantly reduce the incidence of PUBS.