Case Presentation: A 78 year old female with history of chronic kidney disease (CKD) stage 4, diet-controlled diabetes, and bilateral idiopathic ureteral obstruction s/p percutaneous nephrostomies presented with 5 days of changes in urine color. Initially, the patent reported a darker and thicker appearance to her urine that transitioned to a purple color. She denied fevers but had some chills and fatigue. She initially attributed this change in the appearance of her urine to drinking a lot of prune juice, as she also complained of constipation. She denied abdominal pain, flank pain, and decreased nephrostomy tube output. The patient was afebrile and had normal vital signs on presentation. Physical exam was unremarkable except the striking color of the tubing and urine in the nephrostomy bag. Serum white blood cells (WBC) were mildly elevated to 10.6. Creatinine was elevated to 2.0, above her usual baseline of 1.6 to 1.8. Urinalysis showed pH of 8, 4+bacteria, >50 WBCs, 3+ leukocyte esterase, negative for nitrites. Direct examination of the urine sediment did not show crystals. The patient was started on empiric antibiotics and underwent nephrostomy tube exchange with interventional radiology resulting in immediate resolution of abnormal urine color, despite not receiving the first dose of antibiotics until after the procedure. WBC count returned to normal and acute kidney injury resolved. Urine culture ultimately showed mixed bacterial flora and the patient completed a course of oral antibiotics after discharge.
Discussion: Purple urine bag syndrome (PUBS) is a rare condition typically found in elderly chronically catheterized patients and is furthermore associated with female sex, constipation, urinary tract infection, renal failure, and alkaline urine. Despite first being described in 1978, the etiology of PUBS is still somewhat unclear. Most explanations include tryptophan metabolism by gastrointestinal bacteria into indole. Indole is converted via the portal circulation to indoxyl sulfate (indican) leading to indicanuria, where in the presence of certain bacteria and alkaline urine, will break down into indigo and indirubin, turning the urine violet. A similar explanation is used in the blue diaper syndrome first described in 1964. More recently however, it seems that although indicanuria has been associated with PUBS, it is not required. Alkaline urine in contact with elements of the plastic tubing and bag have also been hypothesized to play a role. This case would seem to support the interaction of the tubing with bacterial metabolites contributing to the discoloration given the immediate improvement in the urine appearance post-procedure, even before the administration of antibiotics. E.coli is the most commonly implicated bacteria in PUBS, but there are several others including Klebsiella Pneumoniae, Proteus Mirabilis, and even mixed organisms as in this case. This case is unique in that it reports PUBS in a patient with a percutaneous nephrostomies, which is an even more uncommon characteristic of this already uncommon condition.
Conclusions: Hospitalists and catheterized patients alike should be aware of PUBS as a possible indicator of urinary tract infection. It can be mistaken for hematuria early in the presentation, leading to unnecessary testing and potentially delaying catheter exchange and antibiotic administration.
