The patient may complain or be frightened about the color of his urine; color
may be one component of some urinary complaint, or the color
may be noted incidentally on urinalysis.
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
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.
Porphyrins or eosin dyes fluoresce under ultraviolet light. Eosin turns urine pink or red but fluoresces green.