Purple Pee: Medical Phenomenon

A case of purple urine bag syndrome associated with Providencia rettgeri M A Al-Jubouri and M S Vardhan

Department of Chemical Pathology and Microbiology, St Helens and Knowsley Hospitals NHS Trust, Warrington Road, Prescot, Merseyside L35 5DR, UK

We would like to report this interesting case of an elderly lady (85 years old) who has been passing violet coloured urine over the past four weeks. She is living in a nursing home and has a long term urinary catheter.

There were no other symptoms but her general practitioner was worried about urine discolouration and sent three urine samples to the biochemistry department on three separate occasions to identify the cause of the violet colour. There was no history of intake of medication, food colouring, or special food items that may alter the urine colour.

The urine sample was alkaline (pH 8.5) with a strong smell of ammonia. It was centrifuged and a precipitate of fine blue crystals was identified in the sediment. The supernatant was clear and purple coloured, and was negative for haemoglobin, myoglobin, and porphyrins. At this stage, the purple urine bag syndrome

(PUBS) was suspected and an aliquot was sent to microbiology for culture and sensitivity. There was heavy growth of a coliform species identified as Providencia rettgeri, an ammonia producing bacterium, adding support to the diagnosis of PUBS. This interesting phenomenon in which the urinary catheter of some elderly patients develops intense purple colouration is thought to be caused by indirubin formation.

Various observers stated that indigo producing bacteria, which possess indoxyl sulphatase activity, usually bring about the decomposition of urinary indoxyl sulphate to indigo and indirubin.

Several bacterial species have been reported in association with PUBS including Escherichia coli, Proteus mirabilis, Morganella morganii, Klebsiella pnemoniae, and Providencia stuarti.1–5 Providencia rettgeri was isolated from our patient; to our knowledge this organism has not been reported previously in PUBS cases.

Awareness and prompt identification of this syndrome by biochemistry and microbiology departments should avoid them performing unnecessary tests on such urine samples.