Before going to the causes of purple urine, let’s go through these results,
PH = 8.3, that is alkaline (Normal urinary PH is 5-8 , average is 6). Causes of Alkaline urine are:
- UTI with urease producing organism
- After a meal
- Salicylate intoxication
- Urinary retention, due to obstruction
- Chronic renal failure
- Respiratory alkalosis
- Renal tubular acidosis.
Urease producing organisms are:
- Proteus (able to raise the urinary pH above 8.3)
- Ureaplasma
- Nocardia
- Klebsiella
- Helicobater
- morganella (able to raise urinary PH to 7.3)
- S. Saprophyticus
- Staff aureus (Able to raise urinary PH to 6.9)
The presence of nitrites is very suggestive of bacterial infection.
Other possible causes (false +ve causes):
- Contamination
- Dipstick exposed to air
- Phenazopyridin
Leukocyte esterase is produced by neutrophils and usually it indicates the presence of pyourea.
Causes of Pyourea with -ve culture:
- Chlamydia or Ureaplasma infection
- Balanitis or Urethritis
- TB
- Tumour
- Viral UTI
- Foreign body
- Exercise
- Glomerulonephritis
- Steroids or cyclophosphamide use
The presence of purple urine in a urinary bag is a spot diagnosis of a condition known as Purple Urine Bag Syndrome (PUBS).
Purple urine bag syndrome (PUBS) is the colour of the urinary bag rather than discoloration of urine following urinary catheterization for hours or days.
The condition is caused by infection with bacteria the produces (Indoxyl phosphatase Enzyme). Examples of these bacteria:
- Klebsilla
- Proteus
- E-coli
- Morganella
- Pseudomonas
- Providencia
Tryptophan in diet is metabolized by GIT bacteria to produce Indole. Indole is absorbed and metabolised in the liver to Indoxyl Sulfate and that is excreted in urine.
The presence of bacteria that produces Indoxyl phosphatase Enz in the urinary bag will convert the indoxyl sulfate to Indirubin(Red) and Indigo (Blue). Because these pigments are insoluble, they are attached to a urine bag or catheter, causing purple urine bag syndrome.
Increasing alkalinity of urine leads to crystals formation (Struvite calculi), two conditions must coexist for the formation of these calculi.
- Alkaline urine (pH >7.2).
- The presence of ammonia in the urine.
Urease producing bacteria are associated with the incidence of staghorn calculi. Bacteria will be found around the stone and can re-initiate infection after antibiotic treatment. The Stone will increase in size and might lead to obstructed urinary tract infection. Urease – producing bacteria are also associated with higher incidence of blocked urinary catheters.
The most effective way to prevent crystals coating of catheter was shown to be diluting urine and increasing its citrate concentration.