Q
Which amino acid is implicated in the picture shown?
"Urine bag with purple urine."
© Boentoro et al.
[Source]
(CC BY 4.0
)
Correct Answer:
Explanation
Purple bag syndrome is a rare disorder and is caused by a triad of factors: Constipation, urinary tract infection and catheter in situ.
Initially tryptophan, a dietary amino acid, is digested and metabolised by gut bacteria to produce indole. Indole is converted to indoxyl sulphate in the liver and excreted by the kidneys.
Indoxyl sulphate is then converted in urine by bacterial enzyme indoxyl sulphatase into indoxyl. In alkaline urine indoxyl breaks down into indigo, which is blue in colour, and indirubin, which is red in colour, mixing together to turn purple.
Constipation is required as this prolongs gut transit time and allows for increased levels of indole to be produced and absorbed.
Bacteruria, increased in catheter associated urinary tract infection leads to increased levels of indoxyl sulphatase. Bacteria that can produce these enzymes include Pseudomonas, E.coli, Proteus and Klebsiella.
The catheter allows for increased urinary stasis and there has been suggestion there may be an interaction with the plastic surface in the tubing/bag.
Treatment is of the catheter associated UTI and changing of the bag/catheter.
