What are the minor criteria for the Duke criteria used to diagnose infective endocarditis?

Minor Criteria for Infective Endocarditis (Modified Duke Criteria)

The five minor criteria for diagnosing infective endocarditis are: (1) predisposing heart condition or injection drug use, (2) fever >38°C (100.4°F), (3) vascular phenomena, (4) immunologic phenomena, and (5) microbiological evidence that does not meet major criteria. 1

The Five Minor Criteria in Detail

1. Predisposition

• Predisposing heart condition includes any structural cardiac abnormality that increases endocarditis risk 1
• Injection drug use qualifies as predisposition regardless of cardiac anatomy 1
• Common predisposing conditions include mitral valve prolapse, bicuspid aortic valve, prior infective endocarditis, congenital heart disease, rheumatic heart disease, and prosthetic valves 2, 3

2. Fever

• Temperature >38°C (100.4°F) is required 1
• Fever is present in approximately 81-100% of IE cases and represents the most common presenting symptom 4, 3

3. Vascular Phenomena

• Major arterial emboli to any organ system 1
• Septic pulmonary infarcts (typically seen with right-sided endocarditis) 1
• Mycotic aneurysm formation 1
• Intracranial hemorrhage from septic emboli or mycotic aneurysm rupture 1
• Conjunctival hemorrhages 1
• Janeway lesions (painless hemorrhagic macules on palms/soles) 1

4. Immunologic Phenomena

• Glomerulonephritis (immune complex-mediated) 1, 5
• Osler's nodes (painful nodules on finger/toe pads) 1
• Roth's spots (retinal hemorrhages with pale centers) 1
• Positive rheumatoid factor 1

5. Microbiological Evidence

• Positive blood culture that does not meet a major criterion 1
• This explicitly excludes single positive cultures for coagulase-negative staphylococci and organisms that do not typically cause endocarditis 1
• Serological evidence of active infection with an organism consistent with IE 1

Critical Diagnostic Thresholds Using Minor Criteria

Definite IE can be diagnosed with:

• 5 minor criteria alone (without any major criteria) 1, 6
• 1 major criterion + 3 minor criteria 1, 6
• 2 major criteria (no minor criteria needed) 1

Possible IE is diagnosed with:

• 1 major criterion + 1 minor criterion 1, 6
• 3 minor criteria alone 1, 6

Important Modifications and Caveats

What Was Removed

• Echocardiographic minor criteria were eliminated in the modified Duke criteria because echocardiographic findings are now incorporated exclusively into major criteria 1

Diagnostic Performance

• The modified Duke criteria demonstrate 80% sensitivity across diverse populations including adults, children, injection drug users, and patients with both native and prosthetic valves 6, 7
• The criteria perform better when evaluated at the end of clinical follow-up rather than at initial presentation 8

Clinical Judgment Supersedes Criteria

• The Duke criteria guide diagnosis but do not replace clinical judgment—clinicians may appropriately decide to treat IE even when criteria are not fully met 6, 8
• This is particularly important in culture-negative cases or when prior antibiotic therapy has been administered 1, 8

Common Pitfalls to Avoid

• Do not count a worsening pre-existing murmur as new valvular regurgitation (this does not meet major criteria) 1
• Do not use single positive cultures for coagulase-negative staphylococci as microbiological evidence 1
• Remember that prior antibiotic therapy is the most common cause of culture-negative IE and can reduce diagnostic sensitivity 8
• Obtain at least 3 sets of blood cultures from separate sites before starting antibiotics to maximize diagnostic yield 8