Purple urine bag syndrome
Background
- Rare phenomenon characterized by purple discoloration of the urinary drainage bag and tubing
- Benign reaction in itself, but indicates high bacterial load and Catheter-associated urinary tract infection
- Predominantly affects chronically catheterized, constipated, elderly females (often in nursing homes)
- Caused by specific Gram-negative bacteria producing sulphatase and phosphatase enzymes[ncbi.nlm.nih.gov]
Pathophysiology
- Mechanism:
- Dietary Tryptophan is metabolized by gut bacteria into Indole
- Indole is absorbed and converted to Indoxyl sulfate in the liver
- Indoxyl sulfate is excreted into urine
- Bacteria producing indoxyl sulfatase or phosphatase catalyse the breakdown of indoxyl sulfate into:
- Indigo (Blue pigment)
- Indirubin (Red pigment)
- pigments interact with the polyvinyl chloride (PVC) of the catheter bag to create a
- Risk Factors:
- Chronic Indwelling Catheter (PVC material)
- Constipation (Prolonged gut transit increases bacterial deamination of tryptophan)
- Alkaline Urine (Favors pigment precipitation)
- High bacterial load
- Female gender (shorter urethra, higher UTI risk)
Clinical Features
- Altered Mental Status (if associated with symptomatic UTI/Sepsis)
- Visual alarm (Patient/family/staff often distressed by bright purple color)
- Otherwise usually asymptomatic regarding the discoloration itself
- Common causative organisms (Sulfatase/Phosphatase producers):
Differential Diagnosis
- Rhabdomyolysis (Tea-colored)
- Porphyria (Port-wine colored)
- Medication/Dietary inputs:
- Methylene blue
- Rifampicin (Orange/Red)
- Beets/Blackberries
- Phenolphthalein (laxatives)
Red or Purple Urine
- Hematuria
- Hemoglobinuria
- Porphyria
- Myoglobinuria (rhabdomyolysis)
- Foods
- Blackberries
- Beets
- Blackberries
- Rhubarb
- Food coloring
- Fava beans
- Drugs
- Purple urine bag syndrome
- Uric acid crystalluria (neonates)
Evaluation
- Urinalysis
- Typically Alkaline pH (> 7.0)
- Pyuria/Leukocyte esterase positive
- Urine Culture
- Mandatory to guide susceptibility (high resistance rates in this population)
- Renal function
- Check for AKI/Dehydration
- Evaluate for Sepsis
- Hypothermia/Fever, Hypotension, Tachycardia
Management
- Reassurance
- Explain the benign chemical nature of the discoloration to patient/caregivers
- Source Control
- Exchange the urinary catheter (mandatory to remove biofilm and stained plastic)
- Crucial to reduce gut production of indole
- Antibiotics
- Based on clinical status:
- Asymptomatic Bacteriuria: Antibiotics generally not indicated solely for purple bag; focus on hygiene/catheter exchange
- Symptomatic CAUTI/Sepsis: Empiric broad-spectrum coverage covering Gram-negatives (e.g., Cefepime, Piperacillin-Tazobactam) until sensitivities return
- Note: Many causative organisms (Example: Providencia, Morganella) have intrinsic resistance to common agents like Nitrofurantoin or Colistin
- Based on clinical status: