7.03 Colorful Urine

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What to do:

• Ask about symptoms of urinary urgency, frequency, and crampy pains (suggesting stones), as well as any food colorings, over-the-counter or prescription medications, or diagnostic dyes recently ingested. Ascertain the circumstances surrounding noticing the color: Did the color only appear after the urine contacted the container, or the water in the toilet bowl? Did the urine have to sit in the sun for hours before the color appeared?
• Obtain a fresh urine sample for analysis. Persistent foam suggests protein or yellow foam bilirubin, which should also show up on a dipstick test. A positive dipstick for blood implies the presence of red cells, free hemoglobin, or myoglobin, which can be double-checked by examining the urinary sediment for red cells and the serum for hemoglobinemia. In patients with normal renal function, hemoglobinuria can be distinguished from myoglobinuria by drawing a blood sample, spinning it down, and looking at the serum. Free hemoglobin produces a pink serum which will test positive with the dipstick. Myoglobin is cleared more efficiently by the kidneys, usually leaving a clear serum which tests negative with the dipstick.
• If the urine is red and acidic but does not contain hemoglobin, myoglobin, or red blood cells, suspect an indicator dye such as phenolphthalein (the laxative in ExLax) in which case the red should disappear when the urine is alkalinized with a few drops of KOH. People with a particular metabolic defect produce red urine whenever they eat beets. Blackberries can turn acidic urine red, while rhubarb, anthraquinone laxatives, and some diagnostic dyes will redden urine only when it is alkaline.
• Orange urine may be produced by phenazopyridine (Pyridium) or ethoxazene (Serenium), both of which are used as urinary tract anesthetics to diminish dysuria. Rifampin will also turn urine orange.
• Blue or green urine may be caused by a blue dye such as methylene blue, a component in several medications (Trac Tabs, Urised, Uroblue) used to reduce symptoms of cystitis. A blue pigment may also be produced by Pseudomonas infection
• Brown or black urine (not due to myoglobin or bilirubin) may be caused by L-dopa, melanin, phenacetin, or phenol poisoning. Metabolites of the antihypertensive methyldopa (Aldomet) may turn black on contact with bleach (which is often present in toilet bowls). Contamination with povidone-iodine (Betadine) solution or douche can turn urine brown. Melanin and melanogen, found in the urine of patients with melanoma, will darken standing urine from the air-exposed surface downward.

What not to do:

• Do not allow the patient to alter his urine factitiously. Have someone observe urine collection and inspect the specimen at once.
• Do not let a urine dipstick sit too long in the sample (allowing chemical indicators to diffuse out) or hold the dipstick vertically (allowing chemicals to drip from one pad to another and interfere with reagents).
• Do not be misled by dye in urine interfering with dipstick indicators. Pyridium can make a dipstick appear falsely positive for bilirubin, while contamination with hypochlorite bleach can cause a false positive test for hemoglobin. Also the urobilinogen dipstick (or Erlich reaction) is not adequate for diagnosing porphyria.

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