The Case of the Purple Urine


Here’s a medical conundrum for all of you faithful viewers of “House” out there.

I’m throwing this out there because I have never seen it before. I did some internet searching and think that I came up with the answer (.pdf file) but I’m not positive.

The basic history is that the patient is a bed-bound nursing home resident who has had a conic Foley catheter. The nursing home stated that the urine had started to turn purple over the past 2 weeks. The degree of purple discoloration got more and less, but never went away. It had become particularly bad recently, prompting the call to the ambulance. Notice how even the tubing is purple-colored.

Labs and a UA were sent from the nursing home a week prior and showed some minor renal insufficiency, but were otherwise pretty normal (except for urine color).

Labs done in the ED showed continued renal insufficiency, a mildly elevated WBC count and a UTI. Remember – the patient had no UTI on a UA performed one week prior while she was still having symptoms.

So what is causing the Case of the Purple Urine?

By the way – if you want to use this picture for other purposes, just click on it for a larger version or e-mail me and I’ll send you the high-res version.



  1. Purple urine bag syndrome.
    Often in nursing home females with chronic catheter with uti producing sulphatase or phosphatase.

    Alkaline urine and uti combo.

  2. As Andrew said. Purple Urine Bag syndrome. saw a case the other day- but her UA was grossly nasty.
    Saw one in residency with a guy with bilateral nephrostomies.

  3. Could this be a starch – Iodine reaction? I have seen it when Betadine reacts with the starch used in a roll of plaster used for casting or splinting. Lots of gloves still have starch, and it is common to use a Betadine prep. Just a guess, I have never seen a case of purple urine, but I was a chemistry major…

    • Perhaps the patient had Potassium Iodide to break up mucus? It is excreted in the urine. Cornstarch from gloves can enter the bladder during catheterization and is sometimes seen in a UA.

  4. Purple Urine Bag Syndrome – seen in elderly ladies with long term catheters who are constipated.

    Benign but may indicate a UTI.

    Hope this helps

    Best wishes

    Dr Dean Burns
    SpR EM and ICM

  5. This exact case showed up on our EM trivia night. I thought the resident was joking when he said PUBS, but alas, tis real!

  6. Tryptophan in the diet is metabolized by bacteria in the gastrointestinal tract to produce indole. Indole is absorbed into the blood by the intestine and passes to the liver. There, indole is converted to indoxyl sulfate. Indoxyl sulfate is excreted in the urine. In purple urine bag syndrome, bacteria that colonize the urinary catheter convert the indoxyl sulfate to indirubin and indigo.[1]

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