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The spleen is a small organ about the size of your fist. It's located just below your rib cage on your left side. The spleen helps your body fight infection and filter unwanted material, such as old or damaged blood cells. The spleen also produces red blood cells and certain types of white blood cells.

Typically, an enlarged spleen (splenomegaly) is a sign of an underlying problem. Many conditions — from infections to liver disease and blood cancers — can cause an enlarged spleen. Treatment of an enlarged spleen is usually aimed at the underlying problem.

An enlarged spleen often causes no signs or symptoms. However, some people experience pain in the left upper abdomen or pain that spreads to the left shoulder.

If the enlarged spleen presses against your stomach, you may feel full without eating or after eating only a small amount. If the enlarged spleen removes too many red blood cells from your blood, you may feel tired or weak. Frequent infections or an increased tendency to bleed are possible as well.

Enlarged spleen causes vary, including:

• Viral infections, such as mononucleosis
• Bacterial infections, such as syphilis or an infection of the heart's inner lining (endocarditis)
• Parasitic infections, such as malaria
• Cirrhosis and other diseases affecting the liver
• Various types of hemolytic anemia — a condition characterized by premature destruction of red blood cells
• Blood cancers, such as leukemia and Hodgkin's disease
• Metabolic disorders, such as Gaucher's disease and Niemann-Pick disease

Sometimes pressure on the veins from the spleen or to the liver cause an enlarged spleen. A blood clot in a vein from the spleen or to the liver can have the same effect.

Consult your doctor promptly if you have pain in the left upper abdomen — especially if it's severe or the pain gets worse when you take a deep breath.

An enlarged spleen is usually detected during a physical exam. The doctor can often feel the enlargement by gently examining your left upper abdomen, just under the rib cage.

The diagnosis may be confirmed with blood tests, an X-ray or other imaging studies of the abdomen. For example, an ultrasound or computerized tomography (CT) scan can help the doctor determine the size of your spleen and whether it's crowding other organs. Magnetic resonance imagining (MRI) can be used to trace blood flow through the spleen.

Depending on the circumstances, the doctor may recommend various blood tests or other diagnostic tests to identify what's causing the enlarged spleen.

An enlarged spleen traps and stores an excessive number of blood cells and substances that help blood to clot (platelets). This may clog the spleen and interfere with its ability to function. Eventually, an enlarged spleen may outgrow its own blood supply — damaging or destroying part of the organ. An enlarged spleen is also at risk of rupturing, usually as a result of a blow to the abdomen. A ruptured spleen can cause life-threatening bleeding into the abdominal cavity.

Treatment of an enlarged spleen is usually aimed at the underlying problem. For example, antibiotics or other medications may be used to treat infections.

In some cases, radiation therapy can help shrink an enlarged spleen.

If the enlarged spleen causes serious complications or the underlying problem can't be identified or treated, surgical removal of the spleen (splenectomy) may be an option. In fact, in chronic or critical cases, surgery may offer the best hope for recovery. But elective spleen removal requires careful consideration. You can live an active life without a spleen, but you're more likely to contract serious or even life-threatening infections.

If you have an enlarged spleen, avoid contact sports — such as soccer, football and hockey — and limit other activities as recommended by your doctor. Modifying your activities can reduce the risk of a ruptured spleen.

It's also important to wear a seat belt. If you're in an accident, a seat belt can help prevent injury to your spleen.