An Elderly Man with Purple Urine

Email: hide.soomyung@gmail.com Dear Editor, An 83-year old bedridden man with constipation and hemiparalysis due to subarachnoid hemorrhage was admitted for further examination of anemia and thrombocytopenia. On admission, a Foley urinary catheter, made of 100% silicon, had been placed to measure urine output. Moreover, the urine bag was made of medical-grade polyvinyl chloride. Regarding anemia and thrombocytopenia, the myelodysplastic syndrome was diagnosed based on the dysplasia of erythroblast, megakaryocyte, and chromosomal abnormality in bone marrow aspiration. Consequently, purple urine was first observed at 3 months after urinary catheterization. Urinalysis revealed a pH of 8.5, positive nitrites, and numerous leukocytes and bacteria. Microorganisms like Pseudomonas aeruginosa, Klebsiella pneumoniae, and Escherichia coli were found growing in the urine culture. Thus, the diagnosis of purple urine bag syndrome (PUBS) was made based on the aforementioned characteristic findings. Moreover, the patient had no fever or lower urinary tract symptoms. Furthermore, laboratory findings showed normal leukocyte count and C-reactive protein level. Therefore, no antibiotics were given. PUBS occurs as a result of a chemical reaction in the urine bag. Tryptophan is the metabolite of dietary protein that is catabolized to indole by the intestinal bacteria, absorbed from the intestinal tract, and then converted into indoxyl-sulfate in the liver. Indoxyl-sulfate is excreted into the urine and converted into indoxyl by sulfarase-producing bacteria (e.g., K. pneumonia, Proteus mirabilis, P. aeruginosa, E. coli, Providencia species, and Morganella morganii) (1). Moreover, indoxyl is oxidated into indigo (blue pigment) and indirubin (red pigment) in the presence of alkaline urine. These two pigments do not make the urine purple until they react with the urine bag and tubing.