Blue diaper syndrome

How Come?

Yellow is mellow; other colors result from food, medicine, illness

By KATHY WOLLARD Los Angeles Times Syndicate

Monday, September 8, 2003

My nephew wonders: How come urine is always yellow and never reflects the color of the food or drink we have consumed? asks Annleigh Wallace, of Canada.

Urine's normal color is pale yellow. But the color can change, taking on a rainbow of hues, depending on what we drink or eat, what medicines we're taking and what illnesses we're unlucky enough to have.

Urine is made by the kidneys. The kidneys process 45 to 60 gallons of blood plasma a day -- 720 cups to 960 cups -- to remove about six to eight cups of excess water and waste.

As blood flows through the kidneys, it is processed by tiny filtering units called nephrons. Some water and other substances (sugar, vitamins, amino acids from proteins) are reabsorbed and sent back into the bloodstream for reuse.

What remains behind is urine: 95% water, plus urea (left over after your body digests protein), salts, minerals, creatinine (from muscle breakdown), uric acid, hormone remnants and toxins.

Why is urine yellow? That's because red blood cells don't last forever. Their life spans are about 120 days; worn-out cells are processed by the liver. When the liver breaks down the hemoglobin in a red blood cell, a yellow pigment called urochrome is left over.

Urochrome passes into the bloodstream and is filtered out as a waste product by the kidneys. Presto: yellow urine.

But urine may be almost colorless if you drink a lot of water. On the other hand, if you are sweating heavily and drinking little water, urine becomes concentrated, turning the color of dark amber.

A red tint may indicate a small amount of blood, perhaps from a bladder infection, kidney or bladder stones, or even from running with a full bladder. Any hint of blood in the urine warrants a trip to the doctor.

But some people get reddish-purple urine when they eat beets. If urine is acidic, eating blackberries can turn it red. If urine is alkaline, eating rhubarb can give it that rosy glow. Lead and mercury poisoning can also cause red urine.

Greenish urine can be caused by a urinary tract infection, bile pigment or certain drugs. Spring-green urine can be caused by taking an excess of B vitamins.

Urine with a Windex-blue tint (in babies, "blue diaper syndrome") can mean you inherited a tendency to have high levels of calcium. But it can also mean an infection with the bacteria Pseudomonas.

Dark yellow urine may be a sign of a liver disorder called jaundice. Too many carrots or too much Vitamin C can turn urine Halloween orange. Dyes in foods like candy and soft drinks or in pill coatings can also color urine red, green or blue.

Brown, smoky or black urine can be caused by the liver disease hepatitis, the presence of blood, anti-malaria drugs, copper poisoning, the cancer melanoma, certain laxatives -- even eating too many fava beans.

If your urine is an unusual color, talk to your doctor.

Send questions to How Come?, Discovery Section, Newsday, 235 Pinelawn Road, Melville, NY 11747-4250, or e-mail to howcome@word- detective.com. If answered here, you'll receive "How Come? Planet Earth" by Kathy Wollard and Debra Solomon (Workman Publishing).

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