Colorful Urine

CHAPTER 78

Colorful Urine

Presentation

The patient may complain of 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 painful urination. Include questions about flank or abdominal pain as well as recent ingestion of any food colorings, over-the-counter (OTC) or prescription medications, or diagnostic dyes. Ascertain the circumstances surrounding the change of urine color: Did the color appear only 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 (yellow foam, bilirubin), which should also show up on a dipstick test.

With red urine, 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 that will test positive with the dipstick. Myoglobin is cleared more efficiently by the kidneys, usually leaving clear serum that tests negative with the dipstick. Consider sending the urine for microscopic urinalysis to determine the presence of red blood cells.

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 former laxative in Ex-Lax), in which case the red should disappear when the urine is alkalinized with a few drops of potassium hydroxide (KOH). Fourteen percent of individuals who eat beets produce reddish urine because of the excretion of the pigment betalain. Blackberries can turn acidic urine red, whereas 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, as will carrots, rhubarb, beets, aloe, riboflavin, vitamin A, and vitamin B₁₂.

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. Food Dye and Color Blue Number 1 (FD & C Blue No. 1) has been reported to be absorbed from the gastrointestinal (GI) tract in some patients sufficiently to cause the urine to be dark green.

In the critically ill patient requiring enteral feeding, the practice of adding colored dye (including FD & C Blue No. 1) to the tube feeding to quickly detect occult aspiration can also cause urine discoloration.

Purple urine bag syndrome (PUBS) is a term that has been used to describe the purple discoloration of the collecting bag and tubing that occurs rarely and is predominantly found in elderly bedridden women with chronic urinary catheterization, alkaline urine, and constipation. No specific cause has been found, and it appears to be a benign condition. PUBS has not been demonstrated to have any implication other than the possibility of a urinary tract infection and has not been proven to change the prognosis of patients.

Brown or black urine (not resulting from myoglobin or bilirubin) may be caused by I-dopa, melanin, phenacetin, or phenol poisoning as well as anthraquinones mentioned previously. Metabolites of the antihypertensive methyldopa (Aldomet) may turn black on contact with bleach (which is often present in toilet bowls). Phenytoin (Dilantin) and the statins (Lipitor, Lescol, Mevacor, Pravachol, and Zocor) are also potential causative agents. 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. In addition, the urobilinogen dipstick test is not adequate for diagnosing porphyria.