What are the criteria for diagnosing glomerulonephritis (inflammation of the glomeruli in the kidneys) in a patient with suspected infective endocarditis (infection of the heart valves)?

Glomerulonephritis as a Diagnostic Criterion for Infective Endocarditis

Glomerulonephritis is classified as a minor criterion under "immunologic phenomena" in the modified Duke criteria for diagnosing infective endocarditis, alongside Osler's nodes, Roth's spots, and rheumatoid factor. 1

Role in the Modified Duke Criteria

Glomerulonephritis functions as one of five possible minor criteria used to establish the diagnosis of IE:

• Minor criteria include: 1
  • 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, Janeway lesions)
  • Immunologic phenomena (glomerulonephritis, Osler's nodes, Roth's spots, rheumatoid factor)
  • Microbiological evidence not meeting major criteria

Diagnostic Thresholds Using Glomerulonephritis

Definite IE is diagnosed when: 1

• 2 major criteria are present; OR
• 1 major criterion and 3 minor criteria (glomerulonephritis could be one of these three); OR
• 5 minor criteria (glomerulonephritis could be one of these five)

Possible IE is diagnosed when: 1

• 1 major criterion and 1 minor criterion (glomerulonephritis could be this single minor criterion); OR
• 3 minor criteria (glomerulonephritis could be one of these three)

Clinical Context and Recognition

When evaluating a patient with suspected IE who presents with acute kidney injury, hematuria, or proteinuria, glomerulonephritis should be actively sought as it strengthens the diagnostic probability. 2, 3, 4

Key Clinical Presentations of IE-Associated Glomerulonephritis:

• Acute kidney injury is the most common presenting feature (occurring in the majority of cases) 5
• Hematuria (often macroscopic) and proteinuria 2, 4
• Hypocomplementemia occurs in approximately 56-76% of cases 4, 5
• ANCA positivity may be present in 28-45% of cases, creating diagnostic confusion with vasculitis 6, 5

Histopathological Patterns:

The most common renal biopsy findings in IE-associated glomerulonephritis are: 5

• Necrotizing and crescentic glomerulonephritis (53% of cases) - this is the predominant pattern, contrary to other infection-related glomerulonephritis
• Endocapillary proliferative glomerulonephritis (37% of cases)
• C3-dominant deposition on immunofluorescence is characteristic 4, 5
• Mesangial and/or endocapillary hypercellularity with extensive crescents 6

Critical Diagnostic Pitfalls

IE-associated glomerulonephritis can closely mimic ANCA-associated vasculitis or IgA vasculitis, leading to misdiagnosis in 25-35% of cases. 4, 6 This occurs because:

• ANCA positivity is common (28-45% of cases) 6, 5
• Purpura may be present, mimicking IgA vasculitis 4
• Crescentic glomerulonephritis pattern overlaps with vasculitis 6, 5
• Typical IE manifestations (cardiac murmur, vegetations) may be initially absent 4, 6

To avoid misdiagnosis: 4, 6

• Always obtain blood cultures (at least 3 sets from separate sites) before antibiotics 1, 7
• Perform echocardiography (TTE first, then TEE if negative but suspicion high) 1, 7
• Look for fever (present in 100% of IE-associated glomerulonephritis cases), cardiac murmur (95%), splenomegaly (84%), and embolic phenomena (55%) 4
• Check for hypocomplementemia (76% of cases) - this is more common in IE than in primary vasculitis 4
• Evaluate for predisposing cardiac conditions (present in 80% of cases) 4

Practical Application

When glomerulonephritis is identified in a patient with suspected IE, it contributes one minor criterion toward diagnosis. For example:

• If the patient has positive blood cultures (1 major criterion) plus glomerulonephritis, fever, and a vascular phenomenon (3 minor criteria), this meets criteria for definite IE 1
• If the patient has a vegetation on echocardiography (1 major criterion) plus glomerulonephritis alone (1 minor criterion), this meets criteria for possible IE 1

The presence of crescentic glomerulonephritis with severe acute kidney injury in a patient with predisposing cardiac disease should immediately trigger comprehensive evaluation for IE, even if other typical manifestations are absent. 2, 6