The color purple in just one of two urine bags led to the diagnosis and successful treatment of an infection in a nursing home patient after he was admitted to Hurley Medical Center with the discolored urine.
Three Hurley Internal Medicine physicians described the case of the rare finding for publication in the peer-reviewed journal, BMJ Case Reports, which published the article online Dec. 23, 2015.
Authors include second-year resident Adil Karim MD and faculty physicians Firas Abed MD and Ghassan Bachuwa MD MHSA MS, who also serves as director of the Internal Medicine Residency Training Program at Hurley, which is affiliated with Michigan State University College of Human Medicine.
Purple urine bag syndrome has been described a few times since first reported 30+ years ago, but Hurley’s case also provided a clue to how the infectious organism entered the patient’s body. The patient had nephrostomy tubes and urine bags on both sides, but only one side turned purple – and only the tube and urine bag on the purple side tested positive for Pseudomonas aeruginosa, which was successfully treated with an antibiotic. If the purple urine had been caused by one of the usual suspects, such as recently eating beets or blackberries or taking medications known to cause the color change, both sides would have been affected. The patient also did not have any of the rare metabolic conditions that could produce purple urine.
The tube’s entry site into the patient’s skin did not appear infected, so the hypothesis is that the Pseudomonas organism was harbored in the polyvinyl catheter, where it turned purple after exposure to high levels of tryptophan, which is metabolized in food to indole in the intestines and later converted to indican by the liver. Once indican is broken down in the urine, it becomes indirubin (red) and indigo (blue) in an alkaline environment.
After the infection cleared up, the patient’s nephrostomy tube was changed, and the color of urine remained normal. Prior case reports indicated that recurrence is unlikely if the infection is treated before replacing the tubes.
Source: BMJ Case Report, published online, 23-DEC-2015. Doi: 10.1136/bcr-2015/212913. PMID: 26691115