Introduction: Who Should Undergo Diagnostics

Endocarditis should be suspected in anyone experiencing unexplained fevers, particularly when combined with other concerning symptoms. This is especially important if you have certain risk factors that make you more vulnerable to developing this infection. The disease affects the endocardium, which is the inner lining of the heart’s chambers and valves, and can be fatal if not treated promptly.^[1]

You should seek medical attention as soon as possible if you experience symptoms like persistent fever, chills, night sweats, or fatigue, especially if you fall into a higher-risk group. People with artificial heart valves, damaged heart valves, or other heart defects need to be particularly vigilant, as damaged heart tissue makes it easier for bacteria to attach and grow. Those with a history of previous endocarditis, individuals who inject drugs, people with pacemakers or implantable cardioverter-defibrillators, and those on hemodialysis are also at elevated risk.^[2][3]

It’s important to understand that endocarditis is not a common condition, affecting only about five to seven cases per 100,000 people each year. However, its rarity should not lead to complacency. The infection can progress rapidly, and early diagnosis is vital. If you have undergone recent invasive medical or dental procedures and develop fever or flu-like symptoms, this warrants immediate medical evaluation, as bacteria can enter the bloodstream during such procedures.^[4][5]

The symptoms of endocarditis can be quite variable and may resemble flu symptoms initially, which is why many people delay seeking care. Common signs include fever above 100°F (38.4°C), chills, fatigue, muscle and joint aches, and shortness of breath. Some people also experience chest pain when breathing, swelling in the feet or legs, or unexplained weight loss. Less common but distinctive signs include small spots on the skin, unusual lines under the fingernails, or blood in the urine.^[6]

People with certain heart conditions don’t necessarily have a higher risk of endocarditis. For instance, if you’ve had bypass surgery, a heart attack without complications, or if you have mitral valve prolapse without other issues, your risk is not substantially increased. However, if you have heart valve disease, congenital heart defects, hypertrophic cardiomyopathy (where the heart muscle cells have enlarged), or have had a heart valve replaced or repaired, you should be more alert to potential symptoms.^[5][3]

Diagnostic Methods

When you visit your healthcare provider with suspected endocarditis, the diagnostic process begins with a thorough physical examination and discussion of your medical history. Your doctor will listen carefully to your symptoms and ask about any recent procedures, dental work, or infections you may have had. During the physical exam, they will check for signs of infection such as fever, listen to your heart for abnormal sounds called heart murmurs, and examine your skin and nails for unusual spots or marks that can indicate endocarditis.^[10][5]

The cornerstone of endocarditis diagnosis is blood culture testing. This test is crucial because it helps identify the specific germs causing the infection in your bloodstream. Your doctor will typically draw multiple blood samples from different sites at different times, usually at least two or three separate cultures. This repetition is important because it increases the likelihood of catching the bacteria in your blood and helps rule out contamination. The blood samples are sent to a laboratory where they are placed in special conditions that encourage bacteria or fungi to grow, making them easier to identify.^[10][9]

It’s critical that these blood cultures are taken before you start taking antibiotics. Starting antibiotics too early can make it much harder to identify the organism causing the infection, which in turn makes it difficult to choose the most effective treatment. The results from blood cultures also help determine which specific antibiotics will work best against your particular infection, as different bacteria respond to different medications.^[13]

Blood tests beyond cultures are also performed. A complete blood count can reveal whether you have elevated white blood cells, which indicates infection, or if you have anemia (low red blood cells), which can be a sign of endocarditis. These tests provide supporting evidence but cannot definitively diagnose the condition on their own.^[10]

Imaging tests play a vital role in diagnosing endocarditis. The most important imaging test is an echocardiogram, which uses sound waves to create moving pictures of your heart. This test shows how well your heart chambers and valves are working and can reveal the structure of your heart. There are two main types of echocardiograms used in diagnosing endocarditis. The first is a transthoracic echocardiogram, which is performed by moving a device over your chest. This is the standard, non-invasive version of the test.^[10]

When more detailed images are needed, your doctor may recommend a transesophageal echocardiogram. In this procedure, a flexible tube with a tiny ultrasound device is gently guided down your throat and into your esophagus (the tube connecting your mouth to your stomach). Because the esophagus sits right behind the heart, this test can provide much clearer and more detailed pictures of your heart valves and any abnormalities, such as vegetations (clumps of bacteria, fibrin, and blood cells) that form on infected heart tissue.^[10][2]

An electrocardiogram (ECG or EKG) is another test commonly performed. This quick and painless procedure measures the electrical activity of your heart using sensors attached to your chest and sometimes your arms or legs. While an ECG isn’t specifically used to diagnose endocarditis itself, it can detect if the infection is affecting your heart’s electrical system or causing irregular heartbeats, which is important information for your treatment plan.^[10]

Chest X-rays may also be ordered to check the size of your heart and look for signs of complications. A chest X-ray can show if your heart is enlarged or if fluid has built up in your lungs, which might indicate that endocarditis is affecting your heart’s ability to pump blood effectively. This helps your healthcare team understand the severity of your condition.^[10]

In some cases, additional imaging tests such as MRI (magnetic resonance imaging) or CT (computed tomography) scans may be needed. These tests provide even more detailed images and can help identify complications such as abscesses (pockets of infection) in the heart muscle or blood clots that may have formed and traveled to other parts of your body.^[10]

Urine tests may be performed to check for blood in the urine, which can occur when small pieces of infected material break off from the heart and travel to the kidneys. This finding, along with other test results, helps paint a complete picture of how the infection is affecting your body.^[9]

The diagnosis of endocarditis typically relies on a set of criteria called the Duke criteria, which combine clinical findings, laboratory results, and imaging findings. These criteria classify endocarditis cases as “definite,” “possible,” or “rejected” based on the presence of major and minor criteria. Major criteria include positive blood cultures showing typical bacteria that cause endocarditis, or evidence of heart involvement seen on echocardiography. Minor criteria include fever, certain risk factors (like heart valve disease or intravenous drug use), blood vessel and immune system phenomena, and other supportive laboratory findings.^[8][14]

The diagnostic process may take several days because blood cultures need time to grow in the laboratory, and multiple tests need to be coordinated. However, treatment often begins before all test results are complete, especially if your symptoms suggest a serious infection. Your doctor may start you on broad-spectrum antibiotics that work against many different types of bacteria, and then adjust your treatment once the specific organism is identified.^[13]

Diagnostics for Clinical Trial Qualification

When patients with endocarditis are being considered for enrollment in clinical trials, the diagnostic requirements may be more rigorous and standardized than in routine clinical practice. Clinical trials testing new treatments for endocarditis need to ensure that all participants truly have the condition and that it’s accurately characterized, so they use specific criteria to qualify patients.

For clinical trial enrollment, confirmed diagnosis using the Duke criteria is typically required. This means patients must meet either two major criteria, one major and three minor criteria, or five minor criteria to be classified as having “definite endocarditis.” The Duke criteria have been updated over time, most recently in 2023, to incorporate newer diagnostic techniques such as advanced imaging methods and molecular testing approaches that weren’t available when the original criteria were developed.^[8]

Blood culture results are particularly important for clinical trial qualification. Trials usually require documentation of positive blood cultures with specific organisms known to cause endocarditis, such as Staphylococcus aureus, viridans streptococci, enterococci, or other bacteria commonly associated with the condition. Multiple positive blood cultures drawn at different times strengthen the case for enrollment. Some trials may also use newer microbiological techniques such as enzyme immunoassays or molecular methods like PCR (polymerase chain reaction) to detect organisms that are difficult to grow in standard blood cultures.^[8][14]

Imaging studies, particularly echocardiography, must demonstrate specific findings for clinical trial eligibility. The transesophageal echocardiogram is often preferred because it provides more detailed images and is better at detecting vegetations, abscesses, or valve damage. Trial protocols typically specify the size and characteristics of vegetations that qualify a patient for inclusion. Some newer trials may also incorporate advanced imaging techniques such as cardiac computed tomography or PET scans (positron emission tomography), which can detect inflammation and infection in heart tissue with high precision.^[10][8]

Additional laboratory tests may be required for clinical trial screening beyond what’s done in routine care. These might include specific inflammatory markers in the blood, kidney function tests, liver function tests, and tests to assess your overall health status. Trials need to ensure that participants are healthy enough to safely receive the experimental treatment and can tolerate the study procedures.

Some clinical trials may have specific inclusion criteria related to the type of endocarditis. For example, a study might focus only on patients with native valve endocarditis (infection of the patient’s own heart valve) or only on those with prosthetic valve endocarditis (infection of an artificial replacement valve). The timing of diagnosis may also matter—some trials only accept patients in the early stages of infection, while others may study patients with more advanced disease or those who have failed initial treatment.^[2]

Documentation of any complications from endocarditis is also important for trial qualification. This includes evidence of heart failure, embolic events (where pieces of vegetation break off and travel to other organs), abscesses, or the need for surgery. Trials studying different aspects of endocarditis management may specifically seek patients with or without certain complications.

Before enrolling in a clinical trial, you would typically undergo a comprehensive baseline assessment. This serves both to confirm your eligibility and to establish a starting point against which your response to treatment can be measured. This assessment usually includes detailed blood work, multiple imaging studies, and sometimes additional specialized tests depending on the specific trial protocol.