Q. My mother has had anemia for nearly a year now. However, extensive testing has turned up nothing. I'd like to know if you can suggest any specific tests that may help identify the problem.

A. I'd urge you to keep looking until you have a diagnosis. It's important to find out why your mother has anemia for two reasons: because doing so may identify some underlying problem that needs to be treated and because knowing the cause can be the first step in correcting the anemia.

Anemia means having a decreased amount of red blood cells. Some people refer to this as having a low blood count or "low blood." This is not to be confused with having low blood pressure.

Among their other jobs, your red blood cells carry oxygen throughout your body. If you have severe anemia, you may not have enough oxygen to function normally. You may feel tired, dizzy or a little short of breath. You may look more pale than normal. Your heart may race.

Anemia is a sign of something wrong, not a diagnosis in itself. It typically comes about in one of three ways: bleeding, insufficient production of blood or destruction of blood.

Bleeding may be obvious--in the form of heavy menstrual periods, for example--or subtle--such as losing small amounts inside the intestines. When you lose blood, you also lose the iron in it. So tests for iron deficiency may help pinpoint blood loss as the cause of anemia.

If you have anemia that is due to blood loss, it's important to find the source of the problem. That's because it makes no sense to take iron pills to correct anemia if, for example, the source of bleeding is an undetected cancer in the intestines.

Possible causes of anemia from blood loss include an ulcer, a cancer, a polyp, inflammation of the stomach (gastritis), weak spots in the wall of the intestines (diverticulosis) or blood vessels in the intestines that bleed (A-V malformations).

The second major category of anemia is insufficient blood production by the bone marrow. This problem is commonly caused by chronic health problems such as kidney failure, liver failure and chronic alcoholism. It can also be caused by a lack of folic acid in the body or by damage to the bone marrow resulting from cancer or cancer treatment.

Doctors check for decreased production of red blood cells using various tests. They also search for underlying diseases that may slow the production of blood. If those approaches turn up nothing, doctors might examine blood drawn directly from the marrow through a special procedure called a bone marrow biopsy.

The third major category of anemia is caused by increased destruction of red blood cells. This is known as hemolysis, or hemolytic anemia. There are various kinds of hemolytic anemia. Some, such as sickle cell anemia, are hereditary and permanent conditions. Other types occur later in life. Examples of the latter include those types of anemia that develop as side effects of certain medications and those that result from complications of other diseases, such as cancer or lupus.

In most cases, doctors will be able to narrow the possibilities after taking a history, doing a physical exam and using a few simple blood tests. If your regular physician isn't able to pinpoint a cause, you may need to see a hematologist, a physician who specializes in diseases of the blood.

A systematic search for the cause of anemia will generally lead not only to the proper diagnosis, but also to the right treatment.

Jay Siwek, chairman of the department of family medicine at Georgetown University Medical Center, practices at the Fort Lincoln Family Medicine Center and Providence Hospital in Northeast Washington.