Ask Dr. K: Red or brown urine should be checked by doctor

— By dark, do you mean dark yellow? Or is your urine brown or red?

If your urine is just a dark yellow color at times, especially when you don’t drink enough fluids, then you don’t need to worry. Dark yellow urine is a sign of dehydration. Your urine is dark because your kidneys are doing what they are supposed to do when you are dehydrated: conserving water by making less urine. If this is the case, drink more water —eight 8-ounce glasses each day.

Certain foods and medicines can change urine color and make it smell. Eating asparagus is a good example of a food that causes your urine to take on a distinct odor. Eating beets can turn your urine red and make you worry that you might have blood in your urine. (We doctors have manufactured a medical term for this condition: “beeturia.”)

There are times when a change in the color or smell of your urine warrants a visit to your doctor. For example, see your doctor if your urine is ever red (unless you’ve eaten beets in the past 24 to 48 hours) or brown. This could be a sign of something serious, like a bladder, kidney, blood or liver problem.

— Does it hurt when you urinate? Do you have pain high up on one (or both) sides of your back, weakness, fatigue or fever?

If so, you should see your doctor. You could be having intermittent bacterial infections of your urinary tract. Usually, such infections don't turn urine dark — unless they cause temporary bleeding — but they can. Urinary tract infections often cause pain when you urinate. Other symptoms include having to urinate often and feeling a pressure to urinate.

— Have the whites of your eyes turned yellow?

If so, you could be having liver trouble. When the liver is not working properly, increased amounts of a dark pigment (bilirubin) appear in the blood and in the urine. Your doctor can check your liver function with blood tests.

If you’re concerned, collect a fresh urine sample when you have dark urine. Any kind of container is OK. Bring the urine sample to the doctor within a few hours after collecting it. The doctor will be able to test the urine for blood cells (looking for both bleeding and infection). The urine also can be tested to see if the kidneys are conserving water, as they do when you get dehydrated.

Finally, the urine can be tested for chemicals that turn the urine dark, such as bilirubin or myoglobin. To test for a bacterial infection, it’s best to provide a fresh urine sample collected in a sterile container at the doctor’s office.

Dr. Komaroff is a physician and professor at Harvard Medical School. To send questions, go to AskDoctorK.com, or write: Ask Doctor K, 10 Shattuck St., Second Floor, Boston, MA 02115.