Purple Urine Bag in a Child

A 13-year-old male presented with rapidly progressive renal failure. He was diagnosed with anti-factor H antibody-positive atypical hemolytic uremic syndrome and managed with plasma exchange. He grew Klebsiella pneumoniae in urine, which was sensitive to polymyxin, and the same treatment was initiated. He continued to have fever spikes with pyuria. During the 3^rd week of hospitalization, purple discoloration was noted in the urine collection bag [Figure 1a], while the urine appeared cola-colored [Figure 1b, arrow]. Regrettably, the patient eventually succumbed to multi-organ dysfunction.

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Figure 1:

(a) Purple discoloration of the urine collection bag. (b) Urine is Cola-colored (black arrow), while the bag is stained purple.

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Purple urine bag syndrome (PUBS) is a rare entity seen in the elderly with urinary tract infection. Intestinal bacteria metabolize dietary tryptophan into indole. The liver then converts indole into indoxyl sulfate, which is excreted in urine. Few bacteria, including Klebsiella, further digest indoxyl sulfate into indoxyl through the action of sulfatases and phosphatases, leading to indirubin (red) and indigo (blue). These metabolites accumulate in the plastic tubing and catheter, producing a distinct purple color characteristic of purple urine bag syndrome.¹ In a comprehensive literature review by Sabanis et al., involving 246 reported cases, Purple Urine Bag Syndrome was predominantly observed in elderly adults, with a mean age of 78.9 years, and frequently associated with chronic catheterization, constipation, and CKD.² Though reported in adults, it is rare among children. Recognition of PUBS is important to avoid unnecessary investigation and to reassure families, as the visual appearance can be alarming but does not indicate a severe underlying pathology if managed appropriately.³ PUBS, though rare in children, can be a visual clue to an underlying urinary tract infection.