Woman's Suddenly Purple Pee Had Doctors Guessing

WEDNESDAY, Oct. 30, 2019 (HealthDay News) -- No 'purple rain' jokes, please.

A 70-year-old French woman hospitalized for stroke left her physicians puzzled after her urine took on an unusual hue.

Ten days after receiving a urinary catheter as part of her post-stroke treatment, "her urine appeared purple," reported Drs. Leo Placais and Christian Denier, of Bicetre Hospital in the town of Le Kremlin-Bicetre, France.

However, the vivid plummy color wasn't a sign of anything more serious than a food-microbe interaction, explained one U.S. physician who read over the case study.

"In the spirit of Halloween, even paranormal activity like purple urine can be explained scientifically," said Dr. Guy Mintz. He directs cardiovascular health at Northwell Health's Sandra Atlas Bass Heart Hospital in Manhasset, N.Y.

In this case, the woman developed purple pee because her urine became more alkaline, rather than acidic, Mintz explained. At the same time, there was "an internal chemical reaction between bacteria in her urine and the breakdown of food from her gut," he said.

Specifically, a common food chemical called tryptophan underwent chemical changes within the woman's digestive tract and liver, where it metabolized to form a compound known as indoxyl sulfate, the French researchers said.

"When excreted in the urine, indoxyl sulfate can be broken down by bacterial enzymes to form indigo and indirubin, which are blue and red, respectively, creating the color purple when combined," they reported in the Oct. 30 issue of the New England Journal of Medicine.

Any number of bacteria strains can work on indoxyl sulfate in this way, and so "purple urine is not related to an infection or any form of pathology, but due to a chemical reaction," Mintz explained.

The woman was given more fluids and her urine eventually lost its high alkalinity -- over a few days it turned back to a normal yellow color.

Unfortunately, her stroke left the patient disabled, and she is now in a long-term care facility, according to the report.

More information

There's more on healthy urinary flow at U.S. National Institute on Aging.