• Positive blood cultures taken at different times
• 2-dimensional echocardiography, not always positive for vegetations (transesophageal echocardiography has high sensitivity)
• Leukocytosis in acute endocarditis
• Anemia in subacute endocarditis
• Elevated erythrocyte sedimentation rate
• Decreased C3, C4, CH50 in subacute endocarditis
• Hematuria, microscopic or macroscopic
• Rheumatoid factor in subacute endocarditis
• Serologies for Chlamydia, Q fever (Coxiella) and Bartonella may be useful in "culture-negative" endocarditis

Drugs that may alter lab results: Antibiotics may make blood cultures falsely negative
Disorders that may alter lab results:

• Endocarditis caused by fungi, Chlamydia trachomatis, Chlamydia psittaci, Coxiella burnetii, Bartonella species may be associated with negative blood cultures
• Prolonged incubation of blood cultures is needed in endocarditis caused by fastidious organisms, e.g., HACEK organisms (Haemophilus species, Actinobacillus actinomycetemcomitans, Cardiobacterium hominis, Eikenella corrodens, Kingella species), Brucella species

• Vegetations on the affected endocardium are composed of platelets, fibrin and colonies of micro-organisms. Destruction of valvular endocardium, perforation of valve leaflets, rupture of chordae tendineae, abscesses of myocardium, rupture of sinus of Valsalva, pericarditis may occur.
• Emboli and/or infarction may be found in different body organs. Abscesses and micro-abscesses may be found in different organs. Kidneys may show embolic and/or immune-complex glomerulonephritis.

• Pulmonary ventilation perfusion scan may be useful in right-sided endocarditis
• Computerized axial tomographic scan may be useful in locating abscesses

• Transesophageal echocardiography is useful, especially in prosthetic or bioprosthetic valve endocarditis and S. aureus endocarditis associated with intravascular catheter
• Cardiac catheterization may be indicated to ascertain the degree of valvular damage
• Aortic root injection may be useful when aortic root abscess or rupture of sinus of Valsalva is suspected
• Duke criteria for diagnosis of infective endocarditis
  • 2 major criteria, or
  • 1 major and 3 minor criteria, or
  • 5 minor criteria
• Major criteria
  • Positive blood culture
    • Typical microorganism for infective endocarditis from 2 separate blood cultures: Viridans streptococci, Streptococcus bovis, HACEK group, or community acquired Staphylococcus aureus or enterococci, in the absence of a primary focus, or
    • Persistently positive blood culture. Defined as recovery of a microorganism consistent with infective endocarditis from: blood cultures drawn more than 12 hours apart, or all of 3 or a majority of 4 or more separate blood cultures, with first and last drawn at least 1 hour apart
  • Evidence of endocardial involvement
    • Positive echocardiogram: (a) oscillating intracardiac mass, on valve or supporting structures, or in the path of regurgitant jets, or on implanted material, in the absence of an alternative anatomic explanation, or (b) abscess, or (c) new partial dehiscence of prosthetic valve
    • New valvular regurgitation (increase or change in pre-existing murmur not sufficient)
• Minor criteria
  • Predisposition: predisposing heart condition or intravenous drug use
  • Fever ≥ 38.0°C (100.4°F)
  • Vascular phenomena: major arterial emboli, septic pulmonary infarcts, mycotic aneurysm, intracranial hemorrhage, conjunctival hemorrhage, Janeway lesions
  • Immunologic phenomena: glomerulonephritis, Osler's nodes, Roth spots, rheumatoid factor
  • Microbiologic evidence: positive blood culture, but not meeting major criterion as noted previously or serologic evidence of active infection with organism consistent with infective endocarditis
  • Echocardiogram: consistent with infective endocarditis but not meeting major criterion as previous noted