Urine usually has a harmless cause

A:

It can be troubling to look down and see an unexpected urine color. An abnormal urine color can be an early sign of a serious medical condition. But there's no need to push the panic button yet. Urine can also change color for harmless reasons having to do with the foods you've eaten or medications you've taken.

Most of the time, urine is a pale yellow color because it contains urochrome, one of the substances produced when the body breaks down hemoglobin, a protein in red blood cells.

Urine consists of water and waste products that your kidneys have filtered out of your blood. If your urine turns a dark yellow, it may contain less water and more waste products than usual, which can be an indication that you're dehydrated.

But seeing red or orange instead of the usual yellow can be alarming, especially if there are also symptoms like a burning sensation or pain with urination. To be on the safe side, you should discuss it with your doctor or another clinician.

Following is a brief rundown of some color changes and what they might mean. We'll start with orange, since you asked.

ORANGE: Several medications can turn urine orange, including isoniazid, the mainstay of tuberculosis (TB) treatment; rifampin, another TB drug; high doses of riboflavin, a B vitamin; and phenazopyridine (Pyridium), a drug used in the treatment of urinary tract infection to ease painful urination. Large amounts of carrots or carrot juice may also give urine an orange tinge.

RED: The red of red urine can vary from pink to a very dark red. A simple test can tell if the red color is due to blood in the urine. Inherited conditions such as sickle-cell anemia and thalassemia can cause blood in the urine. So can kidney stones, bladder infections or bladder cancer, and, in men, enlargement of the prostate gland.

Urine can also turn red if it contains myoglobin, an oxygen-binding protein in muscle cells that is similar to the hemoglobin found in red blood cells.

Strenuous exercise can also result in blood getting into the urine. It may come from jostling that damages the bladder in some way. Another possibility is aerobic exercise, which can cause the breakdown of red blood cells.

But there's also a perfectly harmless cause of red urine called beeturia, which can occur after you eat beets.

BROWN OR BLACK: If the red of red urine is dark, it may look brown or even black. In such cases, the causes of brown or black urine may be the same as those of red urine.

But urine can turn truly brown. Bilirubin, another breakdown product of hemoglobin, sometimes builds up in the blood because of liver conditions such as hepatitis and cirrhosis, or a bile duct blocked by gallstones, a tumor, or some other obstacle. If some of that excess bilirubin gets into the urine, the urine can turn a brownish color.

Foods that may turn urine brown include fava beans and rhubarb.

MILKY-WHITE: Urinary tract infections sometimes turn urine a milky-white color. Other causes of whitish urine include uric acid crystals from eating purine-rich foods, such as anchovies, herring and red meat, and phosphate crystals from excess parathyroid hormone. GREEN: Blue pigment can get into urine and mix with the yellow urochrome, making urine look green. It's not an everyday occurrence, but some common medications can cause green, or bluish-green, urine. The anesthetic propofol, the stomach acid drug cimetidine (Tagamet) and the tricyclic antidepressant amitriptyline (Elavil) can have this effect. The discoloration is a harmless side effect.

Green urine can also be a sign of a urinary tract infection or a bacterial infection that has gotten into the blood (bacteremia).

PURPLE: Purple is the only urine color that has a syndrome named after it: purple urine bag syndrome. It occurs when someone has a urinary catheter. Bacteria colonizing the catheter, the collection bag or both produce two substances: indirubin, which is red, and indigo, which is blue. They combine to make a bright purple color.

Discolored urine can be a red-flag warning of a serious medical problem. But it can also be a red herring, the innocent byproduct of certain foods or medicines. If your urine is a surprising hue, ask yourself if there's a simple explanation -- and then ask your doctor for help if you can't find one.

(Submit questions to harvard_adviser@hms.harvard.edu.)

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