Fast Five Quiz: Urine Discoloration

Bradley Schwartz, DO


October 22, 2021

As with other urine color changes, black urine discoloration can stem from causes of red or brown urine depending on urine concentration and the intensity of the color change etiology. A rarely reported but serious cause of brown urine is metastatic melanoma. This can lead to brown or even black urine if melanocytes implant within the urinary tract and slough into the urine and when melanin itself is cleared renally.

Other causes of black urine include laxatives derived from senna leaves and cascara bark, as well as sorbitol, the naturally occurring sugar commonly used as an artificial sweetener. Alpha-methyldopa and levodopa have also been associated with black discoloration of urine.

Poisoning with phenol has been noted to produce black urine, as has copper poisoning. Ingestion of iodine has also been implicated. The skeletal muscle relaxant methocarbamol can also lead to black urine discoloration that varies to blue or green with changes in urine concentration. Alkaptonuria, a genetic condition, can also result in urine darkening upon air exposure due to the accumulation of byproducts that result from disordered tyrosine processing. Disordered hemoglobin production in porphyria can also produce red or brown urine that may appear black after exposure to sunlight.

Read more on malignant melanoma.

This Fast Five Quiz was excerpted and adapted from the Medscape Drugs & Diseases article Discoloration, Urine.

Follow Medscape on Facebook, Twitter, Instagram, and YouTube


Comments on Medscape are moderated and should be professional in tone and on topic. You must declare any conflicts of interest related to your comments and responses. Please see our Commenting Guide for further information. We reserve the right to remove posts at our sole discretion.