From the Guidelines
The diagnostic criteria for infective endocarditis are based on the Modified Duke Criteria, which include major criteria such as positive blood cultures for typical microorganisms and evidence of endocardial involvement on echocardiography, as well as minor criteria like predisposition, fever, vascular phenomena, and immunologic phenomena 1.
Major Criteria
- Blood culture positive for IE: Typical microorganisms consistent with IE from two separate blood cultures, such as Viridans streptococci, Streptococcus bovis, HACEK group, Staphylococcus aureus, or community-acquired enterococci in the absence of a primary focus.
- Evidence of endocardial involvement: Echocardiogram positive for IE, defined as an oscillating intracardiac mass on valve or supporting structures, abscess, or new partial dehiscence of prosthetic valve.
Minor Criteria
- Predisposition: Predisposing heart condition or injection drug use.
- Fever: Temperature >38°C.
- Vascular phenomena: Major arterial emboli, septic pulmonary infarcts, mycotic aneurysm, intracranial hemorrhage, conjunctival hemorrhages, and Janeway lesions.
- Immunologic phenomena: Glomerulonephritis, Osler's nodes, Roth's spots, and rheumatoid factor.
- Microbiological evidence: Positive blood culture but does not meet a major criterion or serological evidence of active infection with organism consistent with IE.
Diagnosis
Diagnosis of IE is definite in the presence of:
- 2 major criteria
- 1 major and 3 minor criteria
- 5 minor criteria It is essential to note that these criteria should be used as a guide for diagnosing IE and must not replace clinical judgment 1.
From the Research
Diagnostic Criteria for Infective Endocarditis
The diagnostic criteria for infective endocarditis are based on the modified Duke's criteria, which include major and minor criteria 2, 3, 4, 5. The major criteria are:
- Typical blood culture results
- Positive echocardiogram results
The minor criteria are:
- Predisposition to infective endocarditis
- Fever
- Vascular phenomena
- Immunologic phenomena
- Suggestive echocardiogram results
- Suggestive microbiologic findings
Application of the Duke Criteria
The Duke criteria are used to classify cases of suspected infective endocarditis into three categories: definite, possible, and rejected 3, 4, 5. The criteria have been shown to be highly specific for ruling out infective endocarditis in patients with acute fever or fever of unknown origin 4. The modified Duke criteria continue to be an important tool for the diagnosis of infective endocarditis, even 20 years after their introduction 5.
Importance of Each Criterion
The importance of each criterion in the diagnosis of infective endocarditis has been evaluated, and it has been shown that the echocardiography major criterion is crucial for the diagnosis, as its absence would result in 43% of cases being classified as possible rather than definite 5. The major microbiological criterion is also important, as its absence would result in only one-third of definite cases being classified as possible. Minor criteria, such as fever and predisposition, contribute to the diagnosis in only 10% of cases.
Laboratory Diagnosis
The laboratory diagnosis of infective endocarditis involves blood cultures, which remain the standard test for microbial diagnosis 6. Directed serological testing and molecular diagnostics, such as 16S rRNA gene PCR/sequencing, may be applied to resected valves to aid in diagnosis. A microbiologic and pathological algorithm for endocarditis diagnosis has been proposed, which takes into account the changing epidemiology and advances in blood culture techniques and new diagnostics 6.
Key Points
- The modified Duke's criteria are used for the diagnosis of infective endocarditis
- The criteria include major and minor criteria, such as typical blood culture results, positive echocardiogram results, predisposition, fever, and vascular phenomena
- The Duke criteria are highly specific for ruling out infective endocarditis in patients with acute fever or fever of unknown origin
- The echocardiography major criterion is crucial for the diagnosis of infective endocarditis
- Blood cultures and molecular diagnostics are important for the laboratory diagnosis of infective endocarditis 2, 3, 4, 5, 6