What Explains This Man’s Apparent Urine Discoloration?

Authors:
Eiyu Matsumoto, MB, and Jennifer R. Carlson, PA-C

Citation:
Matsumoto E, Carlson JR. What explains this man’s apparent urine discoloration? Consultant. 2017;57(12):711.

An 82-year-old man residing in a skilled nursing facility presented to the emergency department with a 1-week history of discolored urine in his collection bag. He had a history of benign prostatic hyperplasia requiring long-term urinary catheter placement, as well as congestive heart failure and hypertension. He also reported having new-onset dysuria. He denied having fever, chills, back pain, nausea, or vomiting. At presentation, he was afebrile with stable vital signs.

His urine appeared to have a purplish discoloration while in the catheter and bag (Figure 1), but the color of the urine changed after being removed from the bag and being placed in a specimen cup (Figure 2). Urinalysis results were positive for both nitrites and leukocyte esterase.

Answer on next page

Answer: Purple Urine Bag Syndrome

Based on his presentation, the patient received a clinical diagnosis of purple urine bag syndrome (PUBS).

Discussion

PUBS, first described in 1978,¹ is a phenomenon associated with bacterial urinary tract infection in persons with indwelling urinary catheters. Although PUBS has been reported as being relatively rare, its prevalence has been estimated to be from 8.3% to as high as 16.7% in patients with long-term urinary catheters.^2-4 Risk factors for PUBS include older age, female gender, chronic constipation, dementia, and a high bacterial load in the urine.^2-8 Cases have been reported in association with hemodialysis for end-stage renal disease and with nephrostomy.^9-11 The bacterial pathogens most often associated with PUBS are Escherichia coli, Klebsiella pneumoniae, Providencia species, Proteus species, Pseudomonas species, Morganella species, and Enterococcus species.^1-7,9-12

The pathogenesis of PUBS begins with the metabolism of tryptophan by gastrointestinal tract bacteria, which eventually leads to the formation of the pigments indigo and indirubin in the urine.³ The combination of indigo, which is blue, and indirubin, which is red, causes the purple discoloration. It is important to note that this discoloration results from an interaction between urine and the urine bag and/or plastic tubing, and that the bag or tubing is purple, not the urine itself.

The prognostic implication of this condition has been controversial. Earlier, PUBS had been thought to be benign.³ However, a number of reported cases have required therapeutic intervention.^5,6,8,12,13 Thus, PUBS is not always benign, and some patients need treatment of catheter-associated urinary tract infection or urosepsis. To date, there is no consensus on the management of PUBS.

Outcome of the Case

The patient’s long-term urinary catheter was exchanged. He was started on nitrofurantoin, 100 mg twice a day for 10 days. Urine cultures grew K pneumoniae, Enterococcus species, and methicillin-susceptible Staphylococcus aureus. His dysuria resolved shortly after starting nitrofurantoin therapy. He was lost to follow-up, so it is unknown whether his PUBS has resolved. 

Eiyu Matsumoto, MB, is a clinical assistant professor in the Department of Internal Medicine, Division of Infectious Diseases, at the University of Iowa Carver College of Medicine in Iowa City, Iowa.

Jennifer R. Carlson, PA-C, is a physician assistant at the Iowa City Veterans Affairs Health Care System in Iowa City, Iowa.

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