How Is Endocarditis Diagnosed?

Your doctor will diagnose infective endocarditis (IE) based on your risk factors, your medical history and signs and symptoms, and the results from tests.

Diagnosis of the infection often is based on a number of factors, rather than a single positive test result, sign, or symptom.

Diagnostic Tests

The results from blood tests, echocardiography, and an EKG (electrocardiogram) can help diagnose IE.

Blood Tests

Blood cultures are the most important blood tests used to diagnose IE. Blood is drawn several times over a 24-hour period. It's put in special culture bottles that allow bacteria to grow.

Doctors then identify and test the bacteria to see which antibiotics will kill them. Sometimes the blood cultures don't grow any bacteria, but the person still has IE. This is called culture-negative endocarditis, and it requires antibiotic treatment.

More standard blood tests also are used to diagnose IE. For example, a complete blood count may be used to check the number of red and white blood cells in your blood. Blood tests also may be used to check your immune system and to check for inflammation.

Echocardiography

Echocardiography is a painless test that uses sound waves to create pictures of your heart. Two types of echocardiography are useful in diagnosing IE.

Transthoracic (tranz-thor-AS-ik) echocardiogram. For this painless test, gel is applied to the skin on your chest. A device called a transducer is moved around on the outside of your chest.

This device sends sound waves called ultrasound through your chest. As the ultrasound waves bounce off the structures of your heart, a computer converts them into pictures on a screen.

Your doctor uses the pictures to look for vegetations, areas of infected tissue (such as an abscess), and signs of heart damage.

Because the sound waves have to pass through skin, muscle, tissue, bone, and lungs, the pictures may not have enough detail. Thus, your doctor may recommend a transesophageal (tranz-ih-sof-uh-JEE-ul) echocardiogram (TEE).

Transesophageal echocardiogram. For this test, a much smaller transducer is attached to the end of a long, narrow, flexible tube. The tube is passed down your throat. Before the procedure, you're given medicine to help you relax, and your throat is sprayed with numbing medicine.

The doctor then passes the transducer down your esophagus (the passage from your mouth to your stomach). Because this passage is right behind the heart, the transducer can get clear pictures of the heart's structures.

EKG

An EKG is a simple, painless test that detects heart's electrical activity. It shows how fast your heart is beating, whether your heart rhythm is steady or irregular, and the strength and timing of electrical signals as they pass through your heart.

An EKG typically isn't used to diagnose IE. However, it may be done to see whether IE is affecting your heart's electrical activity.

For this test, soft, sticky patches called electrodes are attached to your chest, arms, and legs. You lie still while the electrodes detect your heart's electrical signals. A machine records these signals on graph paper or shows them on a computer screen. The entire test usually takes about 10 minutes.