Duke Criteria for Endocarditis

TL;DR

List: Criteria for Endocarditis (Duke) is one of the highest-yield infective cardiology topics in MRCP Part 1. The Duke Criteria combine microbiological, echocardiographic and clinical findings to classify infective endocarditis as definite, possible or rejected. Knowing the major criteria, minor criteria and common examination traps is essential because questions often test interpretation rather than memorisation.

Why this matters

The Duke Criteria remain the internationally recognised clinical standard for diagnosing infective endocarditis. Although imaging technology has evolved, the modified Duke Criteria continue to underpin clinical diagnosis and examination questions.

MRCP Part 1 commonly assesses:

• Recognition of major versus minor criteria

• Interpretation of blood culture results

• Echocardiographic findings

• Predisposing cardiac lesions

• Classification into definite or possible infective endocarditis

Candidates who understand the logic behind the criteria generally answer these questions correctly even when the wording changes.

Core Sections

What are the Duke Criteria?

The Duke Criteria classify infective endocarditis into:

• Definite infective endocarditis

• Possible infective endocarditis

• Rejected infective endocarditis

Diagnosis is based upon combinations of major and minor criteria rather than a single investigation.

The Two Major Criteria

Major Criterion	High-yield MRCP Point
Positive blood cultures	Typical organisms from two separate blood cultures or persistently positive cultures
Evidence of endocardial involvement	Positive echocardiogram showing vegetation, abscess or prosthetic valve dehiscence, or new valvular regurgitation

Typical organisms

Candidates should immediately recognise:

• Staphylococcus aureus

• Viridans streptococci

• Streptococcus gallolyticus (formerly S. bovis)

• HACEK organisms

• Community-acquired enterococci

Repeated isolation of these organisms strongly supports a major criterion.

The Five Minor Criteria

Remember these as clinical evidence supporting infection.

1. Predisposing heart condition or intravenous drug use

Examples include:

• Prosthetic valves

• Previous infective endocarditis

• Congenital heart disease

• Rheumatic valve disease

• Intravenous drug use

2. Fever

Temperature ≥38°C

Simple but commonly forgotten.

3. Vascular phenomena

Examples include:

• Janeway lesions

• Septic pulmonary infarcts

• Arterial emboli

• Splenic infarction

• Mycotic aneurysm

• Intracranial haemorrhage

4. Immunological phenomena

Examples include:

• Osler nodes

• Roth spots

• Glomerulonephritis

• Positive rheumatoid factor

5. Microbiological evidence not meeting a major criterion

For example:

• Single positive culture

• Atypical organism

• Serological evidence

Numbered Revision List: 10 High-Yield Duke Criteria Facts

1. Two major criteria establish definite infective endocarditis.

2. One major plus three minor criteria also establish definite disease.

3. Five minor criteria alone are sufficient for definite infective endocarditis.

4. New valvular regurgitation counts as a major criterion.

5. A changing murmur alone is not a Duke criterion.

6. Vegetation on echocardiography is a major criterion.

7. Positive blood cultures require appropriate organisms and sampling.

8. Intravenous drug use is a minor criterion.

9. Janeway lesions represent vascular phenomena.

10. Osler nodes are immunological phenomena.

These ten facts account for the majority of examination questions.

The Five Most Tested Subtopics

1. Blood culture interpretation

Blood cultures should ideally be obtained before antibiotics.

Typical organisms repeatedly isolated fulfil a major criterion.

MRCP often tests whether contamination (for example coagulase-negative staphylococci in one bottle) should count—it usually does not.

2. Echocardiography

Transthoracic echocardiography is often the initial investigation.

Transoesophageal echocardiography is more sensitive, particularly for:

• Prosthetic valves

• Abscesses

• Small vegetations

3. Clinical signs

Candidates should distinguish:

Janeway lesions

• Painless

• Vascular

versus

Osler nodes

• Painful

• Immunological

This remains a favourite examination distinction.

4. Common organisms

Highest yield organisms include:

• Staphylococcus aureus

• Viridans streptococci

• Enterococcus

• HACEK group

Association questions also appear:

• S. gallolyticus → colorectal neoplasia

• S. aureus → intravenous drug users

5. Diagnostic combinations

Know these combinations thoroughly.

Definite infective endocarditis

• Two major

OR

• One major + three minor

OR

• Five minor

Possible infective endocarditis

• One major + one minor

OR

• Three minor

Practical Example / Mini-Case

A 56-year-old man with known mitral valve prolapse presents with fever for two weeks.

Investigations show:

• Temperature 38.6°C

• Three blood cultures positive for viridans streptococci

• Echocardiography demonstrates a mitral vegetation

Which Duke classification applies?

Answer

Definite infective endocarditis.

Explanation

Major criteria:

• Positive blood cultures

• Vegetation on echocardiography

Minor criteria:

• Fever

• Predisposing valve disease

Two major criteria are sufficient for definite infective endocarditis.

Study Tip Checklist

Before your examination, ensure you can answer these questions without hesitation.

✔ Name the two major criteria.

✔ List the five minor criteria.

✔ Distinguish Janeway lesions from Osler nodes.

✔ Recognise typical blood culture organisms.

✔ Know the diagnostic combinations for definite and possible infective endocarditis.

✔ Identify when TOE is preferred over TTE.

✔ Understand which findings are vascular and which are immunological.

✔ Recognise prosthetic valve endocarditis scenarios.

Common Pitfalls (5 Bullets)

• Confusing Osler nodes (painful, immunological) with Janeway lesions (painless, vascular).

• Assuming any positive blood culture fulfils a major criterion—organism type and persistence matter.

• Forgetting that new valvular regurgitation is a major criterion.

• Believing a changing murmur alone fulfils Duke Criteria—it does not.

• Missing intravenous drug use as a recognised predisposing minor criterion.

FAQs

What is the Duke Criteria used for?

The Duke Criteria provide a standardised clinical method for diagnosing infective endocarditis using microbiological, echocardiographic and clinical findings.

What are the two major Duke Criteria?

The two major criteria are:

1. Typical positive blood cultures.

2. Evidence of endocardial involvement on echocardiography or new valvular regurgitation.

How many minor criteria are there?

There are five categories of minor criteria:

• Predisposition

• Fever

• Vascular phenomena

• Immunological phenomena

• Microbiological evidence not meeting a major criterion

Is echocardiography always a major criterion?

Only when it demonstrates evidence of endocardial involvement such as vegetation, abscess or prosthetic valve dehiscence.

Why is this topic important for MRCP Part 1?

Questions commonly require candidates to interpret combinations of clinical findings rather than simply recall definitions, making Duke Criteria one of the highest-yield infective cardiology topics.

Ready to start?

Mastering the Duke Criteria is only one component of infective disease revision. Continue building your knowledge with the MRCP Part 1 overview, reinforce learning using the Free MRCP MCQs, and test yourself under exam conditions with mock tests from Crack Medicine.

Sources

1. MRCP(UK). https://www.mrcpuk.org/

2. European Society of Cardiology. 2023 ESC Guidelines for the Management of Infective Endocarditis. https://academic.oup.com/eurheartj/article/44/39/3948/7243107

3. Habib G, et al. European Heart Journal.

4. Baddour LM, et al. American Heart Association Scientific Statement on Infective Endocarditis.

5. Oxford Handbook of Clinical Medicine (latest edition).