What Else Turns the Urine Purple?
One unique aspect of purple urine bags syndrome is the permeation of the pigment into the plastic bag. Of course this makes sense if one envisions the plastic bag and tubing—the collection system—as a conduit exposed to a substantial volume of urine en route from the kidneys to being flushed, during the lifetime of the disposable plastic element. Any substance dissolved in the urine that has an affinity for plastic can be, de facto, selectively extracted, and thereby become either more concentrated and hence more visible, or simply more conspicuous when separated from other urinary pigments.
The myriad causes of abnormal color of the urine (not precisely what we see here, which is more the bag than the urine) were collected by 2 nephrologists in 1988. For purple, they mention porphyrins, especially under UV light; chlorzoxazone(Drug information on chlorzoxazone); and, in the presence of alkalinization, phenolphthalein, well known both as an acid-base indicator and as a bowel stimulant. The more familiar red color provided dramatic proof of laxative abuse that had been denied: add a quantity of base to a clear container of the patient's urine, in which the surreptitiously ingested laxative must have been excreted, and watch it turn red! The withdrawal of phenolphthalein from the market because of concerns about carcinogenesis has made the practice of medicine a little less vivid than it used to be. The list of causes of red, red-orange, and red-to-pink urine, which far exceeds the "blood and infection" that would come to mind instantly, remains worth a perusal.4
Purple urine bags syndrome continues to be reported because it has not yet become familiar. Studies that claim a 10% prevalence in patients with long-term urethral catheters seem discordant from the individual experience of many physicians, this one included, but nurses may note it more often. I mentioned purple urine bags syndrome to the nurses when cultures from a patient with non-purple urine and bag showed more than 100,000 colonies per mL of Providencia stuartii. The response was, "Yes, I saw that in a young paraplegic patient who had a catheter and frequent urinary tract infections, but I never knew what it was."
The science now exists for us to connect the otherwise confusing pieces of this puzzle, and to understand why the changing of tubing and the administration of appropriate antibacterials, when indicated, will lead to fading (Figure) and then disappearance of the extraordinary discoloration.
1. Barlow GB, Dickson JAS. Purple urine bags. Lancet. 1978;1:220-221.
2. Payne B, Grant A. Purple urine bags. Lancet. 1978;1:502.
3. Sammons HG, Skinner C, Fields J. Purple urine bags. Lancet. 1978;1:502.
4. Raymond JR, Yarger WE. Abnormal urine color: differential diagnosis. Southern Med J. 1988;81:837-841.
5. Dealler SF, Hawkey PM, Millar MR. Enzymatic degradation of urinary indoxyl sulfate by Providencia stuartii and Klebsiella pneumoniae causes the purple urine bag syndrome. J Clin Microbiol. 1988;26:2152-2156.
6. Dealler SF, Belfield PW, Bedford M, et al. Purple urine bags. J Urol. 1989;142: 769-770.
7. Rahav G, Pinco E, Silbaq F, Bercovier H. Molecular epidemiology of catheter-associated bacteriuria in nursing home patients. J Clin Microbiol. 1994;32:1031-1034.
8. Al-Jubouri MA, Vardhan MS. A case of purple urine bag syndrome associated with Providencia rettgeri. J Clin Pathol. 2001;54:412.
9. Mantani N, Ochiai H, Imanishi N, et al. A case-control study of purple urine bag syndrome in geriatric wards. J Infect Chemother. 2003;9:53-57.
10. Coquard A, Martin E, Jego A, et al. Purple urine bags: a geriatric presentation of lower urinary tract infection. J Am Geriatr Soc. 1999;47:1481-1482.
11. Ribeiro JP, Marcelino P, Marum S, et al. Case report: purple urine bag syndrome. Crit Care. 2004;8:R137.
12. Wang IK, Ho DR, Chang HY, et al. Purple urine bag syndrome in a hemodialysis patient. Intern Med. 2005;44:859-861.
13. Tang MW. Purple urine bag syndrome in geriatric patients. J Am Geriatr Soc. 2006;54:560-561.
What Else Turns the Urine Purple?