Most of the time, urine is a pale yellow color because it contains urochrome, one of the substances produced when hemoglobin gets broken down. Hemoglobin is the protein in red blood cells that sticks to oxygen so it can be ferried around the body.

Occasionally, though, urine turns a very different color. Men may notice the change as their urine enters the toilet bowl or urinal. Women may be more likely to observe it after wiping. 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. The alarm may be justified: an abnormal urine color can be an early sign of a serious medical condition. To be on the safe side, it should be discussed with a doctor or another clinician.

But don't push the panic button. Urine can also change color for harmless reasons having to do with the foods you've eaten or medications you're taking. And colors other than red and orange are very unusual.

Following is a brief rundown of some of the color changes and what they might mean.

Dark yellow

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've gotten dehydrated from not drinking enough fluid.

Red

As a review article about abnormal urine color published in 2012 in the Southern Medical Journal points out, the red of red urine can vary from pink to a very dark red. A simple test can tell if the red color is from hematuria, the medical term for blood in the urine. 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.

Any number of problems affecting the urinary system (the two kidneys and ureters, the bladder, and the urethra) can allow blood to get into the urine. The long list includes kidney stones, bladder infections or bladder cancer, and, in men, enlargement of the prostate gland (benign prostatic hyperplasia).

Strenuous exercise can also result in blood getting into the urine. Why it happens isn't certain, but it may come from jostling that damages the bladder in some way. Another possibility: aerobic exercise can cause the breakdown of red blood cells.

Inherited conditions that affect red blood cells and hemoglobin, like sickle-cell anemia and thalassemia, can cause hematuria. A rare set of conditions known collectively as porphyrias can also turn urine reddish or brown.

But there's also a perfectly harmless cause of red urine called beeturia, which can occur after you eat beets. For that to happen, the conditions in your stomach and intestines must be just right or else the pigment responsible, called betalain, loses its color. Iron deficiency and eating beets with foods that contain a substance called oxalate make beeturia more likely to occur.

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, like 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. Hemolytic anemia, when too many red blood cells get broken down at the same time, also produces a bilirubin surplus that may taint urine.

Melanoma, the most serious type of skin cancer, can, in rare instances, put melanin, the pigment that darkens skin, in circulation, and some of that pigment may wind up in the urine. Foods that may turn urine brown include fava beans and rhubarb.

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.

Milky-white

Urinary tract infections sometimes turn urine a milky-white color because they provoke an immune response that unleashes a flood of white blood cells. Other causes of whitish urine include uric acid crystals from eating purine-rich foods, such as anchovies, herring, and red meat (lamb, beef, and pork), and phosphate crystals from excess parathyroid hormone.

Blue

Methylene blue, a dye used in various diagnostic tests, can turn urine blue. Methylene blue has antimicrobial properties, so it's sometimes found in medications and home remedies. It's also used by itself to treat some rare medical conditions. Inherited conditions like blue diaper syndrome and Hartnup disease can result in blue urine.

Green

If blue pigment gets into urine, the color is often green because the blue mixes with the yellow urochrome that's naturally present. It's not an everyday occurrence, but there are case reports of many common medications causing green — or bluish-green — urine, including the anesthetic propofol, the stomach acid drug cimetidine (Tagamet), and the tricyclic antidepressant amitriptyline (Elavil). The discoloration is a harmless side effect. Asparagus sometimes adds a greenish tinge that's also perfectly harmless. But green urine can 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 a substance called indirubin, which is red, and indigo, which is blue, and they combine to make a bright purple color.

A pair of Israeli doctors reported a case involving purple urine in 2012 in The Journal of the American Medical Association. The accompanying photo showed a bluish-purple catheter and collection bag. They reported that when the patient's catheter was replaced, her urine became clear.

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