Duke Creteria Infective Endocarditus
Also written as Modified Duke Criteria, IE Diagnostic Criteria.
The Modified Duke Criteria are a standardized diagnostic tool used to evaluate suspected infective endocarditis. They stratify patients into 'Definite', 'Possible', or 'Rejected' categories based on clinical, microbiological, and echocardiographic findings.
Diagnostic Framework
Diagnosis requires a combination of major and minor criteria. A 'Definite' diagnosis is reached with 2 major criteria, 1 major and 3 minor criteria, or 5 minor criteria.
- Definite IE: Pathological or clinical evidence
- Possible IE: 1 major and 1 minor, or 3 minor criteria
- Rejected: Alternative diagnosis or symptom resolution within 4 days
Major Criteria: Microbiology
Evidence of typical organisms from blood cultures is a hallmark of endocarditis.
- Typical organisms: S. viridans, S. bovis, or HACEK group found in two separate blood cultures
- Persistently positive cultures: Organisms recovered from cultures drawn >12 hours apart
- Coxiella burnetii: Single positive culture or IgG antibody titer >1:800
Major Criteria: Imaging
Echocardiography identifies structural damage or vegetations on cardiac valves and endocardial surfaces.
- Echocardiogram: Presence of vegetation, abscess, or new valvular regurgitation
Minor Criteria
These include predisposing factors and systemic manifestations of the infection.
- Predisposition: Heart condition or IV drug use
- Fever: Temperature ≥38.0°C
- Vascular phenomena: Emboli, mycotic aneurysms, or Janeway lesions
- Immunological phenomena: Glomerulonephritis, Osler nodes, or Roth spots
- Microbiological evidence: Positive cultures not meeting major criteria
Often confused with
- Acute Rheumatic Fever: Both present with fever and murmur, but Rheumatic Fever follows a strep throat infection and has specific Jones criteria findings like chorea.
- Systemic Lupus Erythematosus (SLE): Can cause Libman-Sacks endocarditis (sterile vegetations) and skin rashes that mimic embolic phenomena.
- Atrial Myxoma: A benign heart tumor that can cause systemic emboli and constitutional symptoms similar to IE.
Where results can mislead
- Prior Antibiotic Use: Can result in 'Culture-Negative Endocarditis', making it difficult to satisfy the major microbiological criterion.
- Early Disease: Transthoracic Echocardiogram (TTE) may be negative in up to 30% of cases, especially if vegetations are small (<2mm).
- Right-sided Endocarditis: Often seen in IV drug users; peripheral stigmata like Osler nodes are frequently absent because emboli go to the lungs rather than the systemic circulation.
Questions an examiner may ask
- List three minor criteria according to the Modified Duke classification.
- How does the presence of a prosthetic valve change the diagnostic threshold for endocarditis?
- Distinguish between Osler nodes and Janeway lesions in the context of physical exam findings.
When to seek help
- New or changing heart murmur
- Persistent high fever with night sweats
- Sudden weakness or numbness (embolic stroke)
- Small, painful nodules on fingers or toes
- Shortness of breath or worsening leg swelling
Quick questions
What constitutes a 'Definite' diagnosis using Duke Criteria?
A diagnosis is definite if there are 2 major criteria, 1 major and 3 minor criteria, or 5 minor criteria met.
Why was the 'Modified' Duke Criteria created?
It was updated to include S. aureus bacteremia as a major criterion regardless of source and to incorporate newer imaging modalities like TEE and Q-fever serology.
What are the common organisms identified in major criteria?
Viridans group streptococci, Streptococcus gallolyticus (bovis), HACEK group, Staphylococcus aureus, and Enterococci.