What Is Possible Infective Endocarditis? Duke Criteria

When your diagnostic results indicate “possible” infective endocarditis, it means your care team suspects you might have a heart valve infection, but the current evidence does not fully meet the strict criteria for a “definite” diagnosis. It is treated as an important working diagnosis—not as absolute proof of infection, but certainly not something to dismiss ^[1].

When to Seek Immediate Help: A “possible” diagnosis means your condition requires close medical attention. Do not wait for a scheduled outpatient scan or follow-up if your symptoms worsen. Seek emergency medical care immediately if you experience severe or rapidly worsening shortness of breath, fainting, confusion, chest pain, blue lips, new weakness, or signs of shock.

How the Duke-ISCVID Classification Works

To diagnose infective endocarditis, doctors use a clinical framework called the Duke-ISCVID criteria (International Society for Cardiovascular Infectious Diseases), which was updated in 2023 to improve accuracy ^[2]. It is not a numerical percentage score, but rather a checklist of specific findings divided into two categories:

• Major criteria: These are the strongest signs of infection. They include finding specific endocarditis-causing bacteria in multiple separate blood culture draws, or clear evidence of valve damage/infection on imaging ^[3].
• Minor criteria: These are supporting clues that have alternative explanations on their own. They include having a predisposing condition (like an artificial/prosthetic valve or a pacemaker) ^[3], a fever of 38°C (100.4°F) or higher, vascular phenomena (issues like blood vessel blockages or certain skin spots), or immunologic phenomena (like infection-related kidney inflammation).

Doctors classify your condition based on combinations of these criteria. A “definite” diagnosis requires strict combinations: either two major criteria, one major plus three minor criteria, or five minor criteria. A “possible” diagnosis means you meet some criteria—specifically, either one major plus one minor criterion, or three minor criteria—but fall short of the “definite” threshold.

What This Means for Your Treatment

A “possible” classification does not automatically mean you will be placed on antibiotics ^[4]. Treatment decisions depend heavily on how stable you are and your overall clinical picture:

• If you are clinically stable: Doctors will generally wait to collect multiple sets of blood cultures before starting antibiotics. This prevents premature treatments from hiding the specific bacteria causing the infection ^[4].
• If you are severely ill or unstable: If you have sepsis or dangerous symptoms, doctors will draw blood cultures and then immediately start empiric antibiotics (broad-spectrum medications that treat many types of bacteria) without waiting for the culture results ^[4].

Do not start, stop, or change antibiotics without your treating team’s guidance. If intravenous (IV) antibiotics are necessary, the treatment course often lasts for several weeks. During this time, your team will carefully monitor your kidney function, liver function, and drug levels to manage any side effects.

Doctors rely on multidisciplinary teams—including infectious disease specialists, cardiologists, and cardiac surgeons—to manage suspected endocarditis ^[5]. A surgical consultation does not mean you will definitely need surgery; it ensures experts are monitoring you to prevent complications while the diagnosis is clarified ^[6].

Next Steps: Gathering More Information

To better understand your condition, your doctors will likely order further tests. While these tests help guide care, it is important to know that they may not always completely confirm or rule out the infection immediately.

• Advanced Imaging: If you have only had a standard transthoracic echocardiogram (TTE, an ultrasound on the outside of the chest), doctors may order a transesophageal echocardiogram (TEE). A TEE involves fasting, mild sedation, and passing a specialized ultrasound probe down your esophagus for a much clearer view of the heart valves ^[7].
• Complementary Scans: The 2023 update includes 18F-FDG PET/CT or cardiac CT scans. PET/CT is particularly helpful for spotting infections around artificial (prosthetic) valves or cardiac devices, though it can be complicated by normal inflammation if you recently had heart surgery ^{[3] [8]}.
• Blood Cultures and Molecular Tests: If your initial blood cultures were positive, doctors will repeat them to ensure the bacteria are clearing from your bloodstream. Sometimes, patients have culture-negative endocarditis (where no bacteria grow, often because they took antibiotics before the blood draw). In these selective cases, doctors may use advanced molecular testing or serology to try to identify the organism ^[3].

Your care team will continuously reassess these test results alongside your symptoms to adjust, narrow, or stop your treatment appropriately.