This case describes a 48-year-old woman taking mesalazine for Crohn’s disease who presented to the emergency department with intermittent, dark reddish-brown urine, interpreted as haematuria. The presentation of macroscopic haematuria, which ranges from light, rose-coloured urine to frank red blood to a dark brown, raises clinical concern for an undiagnosed glomerulonephritis, urinary tract infection or malignancy. Such a presentation thus often triggers a cascade of further blood and urine testing and radiological investigations, a process which can cause significant anxiety and may expose the patient to unnecessary risks. It was soon established that the “haematuria” was in fact a chemical reaction between renally excreted mesalazine and household bleach in the toilet bowl — a phenomenon previously described in several case reports, but relatively unfamiliar amongst clinicians. 1-3 Raising clinician awareness of this unusual occurrence so patients on mesalazine can be appropriately counselled is likely to improve patient outcomes by reducing distress and preventing unnecessary investigations and treatment.
Lee et al. (Sun,) studied this question.