Diagnosing endocarditis is complicated by the condition’s large number of possible signs and symptoms. A physician may suspect endocarditis based on a patient’s medical history and physical symptoms upon examination. However, endocarditis may present the same symptoms as pneumonia, heart attack or many other conditions. Furthermore, because it can be caused by a variety of bacteria, which are difficult to isolate, many physicians begin their diagnosis by ruling out other causes. In general, if a constellation of symptoms is present and there is no other known infection or condition, a physician may narrow down the diagnosis to endocarditis.

The two most common tests to confirm this diagnosis are blood tests and echocardiogram. Blood tests or cultures are used to detect the presence of bacteria, identify the bacteria and determine which antibiotics they are sensitive to. A sample of blood will be placed in a culture bottle containing a nutrient broth that supports the growth of the type of bacteria that commonly causes endocarditis. If the endocarditis is acute, these samples will be taken over a period of an hour. If the endocarditis is subacute, the samples may be taken over a period of days and treatment may be delayed. The object is to culture and isolate the organisms so physicians can identify which organism is responsible for the infection.

It is not easy to capture the bacteria in a blood culture, and physicians have a better chance of doing so when people have a fever, which may happen when large numbers of bacteria enter the bloodstream. Other blood samples may be taken to detect the presence of anemia. In about 2 percent to 5 percent of cases of bacterial endocarditis, the blood cultures are negative. This is especially true among patients who have already been treated with antibiotics. Therefore, negative blood cultures do not necessarily rule out endocarditis, and depending on the other signs and symptoms present, the physician may go ahead and recommend medical therapy.

The blood culture is frequently followed by an echocardiogram, especially among patients at moderate to high risk of endocarditis. This painless, noninvasive test uses sound waves to visualize the structures and functions of the heart. A moving image of the patient’s beating heart is displayed on a video screen, where a physician can study and measure various factors. These include the heart’s thickness, size, function and any buildup of vegetations (clumps of trapped bacteria or fungi layered with platelets, fibrin and immune cells) that may be present. The image also shows the motion pattern and structure of the four heart valves, revealing any potential leakage (regurgitation), narrowing (stenosis) or damage caused by infection.

In some cases, the physician may need to do a minimally invasive transesophageal echocardiogram. During this test, a flexible transducer is placed down the throat and into the esophagus to create very clear images of the heart and valves without interference from the chest wall or lungs. The goal is to determine if the heart valves have been compromised by the infection.

Other tests that may be ordered during the initial screening might include an electrocardiogram, which measures the heart’s electrical rhythms, or a chest x-ray, which can reveal blood or fluid that has backed up into the lungs.