A king is one who has few things to desire and many things to fear. -
Francis Bacon

I n 1812, physicians caring for England's "Mad" King George III reported a bluish tinge to the King's urine that left "a pale blue ring upon the glass near the upper surface."¹ At the same time the blue urine was reported, it was also noted that the King was suffering from one of his frequent severe bouts of constipation and vomiting. Although this phenomenon stymied King George's physicians, modern science has a theory that explains King George's "royal indigo" urine is the result of normal bacterial action in the digestive process.

An essential amino acid called tryptophan is not found in the body but must be obtained from dietary intake (commonly found in turkey). It is metabolized by intestinal flora. Because the King was constipated, putrefaction of bowel contents led to indole formation from dietary tryptophan by the normal intestinal flora. The normal flora of the colon includes species with tryptophanase, an enzyme that catalyzes the formation of indole, pyruvic acid, and ammonia from dietary trytophan. Indole is rapidly absorbed from the colon into the portal circulation and converted in the liver to indoxyl sulphate after a series of detoxification transformations. Indoxyl sulphate is excreted in the urine and digested into indoxyl by the enzyme sulphatase/phosphatase, which is produced by certain bacteria such as Pseudomonas aeruginosa, Proteus mirabilis, Morganella morganii, and Escherichia coli. Indoxyl changes into indigo (blue) and indirubin (red) in the presence of alkaline urine, creating a purple color.

It is likely that sulphatase enzyme created by bacteria in the King's urinary tract or present on his chamber pot caused indoxyl to be slowly released by oxidization, which then became indigo blue and precipitated onto the porcelain of his chamber pot to the utter amazement of his physicians.

Today, even though theories exist to explain it, the etiology of Purple Urine Bag Syndrome (PUBS) remains controversial. Many believe it is associated with constipation,^2-4 alkaline urine,^1-3 and bacteria in the urinary tract that produce the enzyme sulphatase/phosphatase. It occurs in chronically catheterized female patients more frequently than in catheterized males. Purple Urine Bag Syndrome is also known to occur in patients with a urinary stoma. Chronic constipation is commonly associated with bacterial overgrowth in the colon in which tryptophan has been converted to indol. A study conducted in Japan⁵ suggested that a higher bacterial yield in urine, in combination with other facilitating factors such as female gender and alkaline urine, acts as the most important factor in the development of PUBS.

Purple Urine Bag Syndrome is a rare occurrence, is often asymptomatic, and appears to be benign. However, all the patients in one study of PUBS⁴ were suffering from constipation and had alkaline urine, making them more susceptible to urinary tract infection. Even though these patients showed no clinical signs of urinary tract infection, specific micro-organisms were identified in their urine that produced the sulphatase/phosphatase enzyme.

A classic case of PUBS presents when the patient's bedside drainage bag, catheter tubing, or urostomy pouch turns reddish blue or purple. It is thought that the indirubin (red) is dissolved in the plastic of the drainage bag, ostomy pouch, or urinary catheter, and that indigo (blue) crystals in the urine coat the bag or catheter's inner surfaces, combining to form the characteristic purple color. The longer the drainage system is used, the deeper the purple color becomes. A strong odor often is associated with PUBS.⁶

Nursing Action
Nurses caring for patients with an indwelling catheter or a urinary stoma should be vigilant for PUBS. Interventions (eg, high daily doses of vitamin C as ordered) to keep the urine acidic should be included in the plan of care as well as efforts to prevent constipation and maintain adequate hydration. Urinary pouches, catheters, urinary tubing, and bedside drainage bags should be changed regularly, and more frequently than usual if PUBS is noted. Good hygiene, including appropriate hand washing, peristomal skin care, and catheter care, should be maintained not only by the nursing staff, but also by the patient, caregiver, or other family support. Because PUBS can be alarming to staff, visitors, patients, and their families, appropriate education should be instituted regarding the syndrome and necessary precautionary steps taken to avoid a urinary tract infection.

Purple Urine Bag Syndrome has stymied physicians since 1812. While scientists believe they know more about the syndrome today, it still remains a subject requiring further investigation. - OWM

The Ostomy Files is made possible through the support of ConvaTec, A Bristol-Myers Squibb Company, Princeton, NJ