What diagnostic tests are used to diagnose rheumatic fever?

Diagnostic Tests for Rheumatic Fever

The diagnosis of acute rheumatic fever is primarily clinical, based on the revised 2015 Jones Criteria which require documented evidence of preceding Group A Streptococcal infection plus specific major and minor manifestations, with echocardiography now playing a central role in detecting carditis. 1, 2

Essential Diagnostic Components

1. Evidence of Preceding Streptococcal Infection (Required)

Documentation of recent Group A Streptococcal pharyngitis is mandatory for diagnosis, except in rare scenarios such as isolated chorea or indolent carditis. 1, 3 Laboratory confirmation includes:

• Antistreptolysin O (ASO) titer - the primary antibody marker 4
• Additional streptococcal antibodies when ASO is equivocal: antihyaluronidase, antideoxyribonuclease B, and antistreptokinase 4

2. Jones Criteria Application

The American Heart Association's 2015 revision stratifies populations into low-risk versus moderate-to-high-risk groups, with different diagnostic thresholds for each. 1, 5

For diagnosis, you need:

• Two major criteria, OR
• One major plus two minor criteria 1, 3

Major Criteria:

• Carditis (clinical or subclinical by echocardiography)
• Polyarthritis (or monoarthritis in high-risk populations)
• Chorea
• Erythema marginatum
• Subcutaneous nodules 1, 5

Minor Criteria:

• Polyarthralgia (or monoarthralgia in high-risk populations)
• Fever ≥38.5°C (low-risk) or ≥38.0°C (moderate-to-high-risk)
• Elevated acute phase reactants
• Prolonged PR interval on ECG 1, 5

3. Echocardiography - The Critical Imaging Test

Standard echocardiography with Doppler is now the gold standard for detecting carditis and should be performed in all suspected cases, even without clinical signs of heart involvement. 1, 6

• Echocardiography detects subclinical carditis - a major 2015 revision that significantly impacts diagnosis, as many patients have valve involvement without audible murmurs 1, 6
• Diagnosis uses 2012 World Heart Federation criteria for rheumatic heart disease classification (definite vs. borderline) 1
• Handheld echocardiography shows high sensitivity (0.87) and specificity (0.98) compared to standard echocardiography, making it a viable alternative in resource-limited settings where standard equipment is unavailable 1

Critical caveat: Cardiac auscultation alone has very low sensitivity for diagnosing carditis and should never be relied upon as the sole method for excluding cardiac involvement. 1

4. Acute Phase Reactants

Elevated inflammatory markers are essential minor criteria and help distinguish active disease:

• Erythrocyte sedimentation rate (ESR) - typically >60 mm in the first hour in acute rheumatic fever 7
• C-reactive protein (CRP) - shows rapid elevation and is useful for monitoring treatment response 4
• Combined ESR and CRP measurement provides the most useful information in chronic inflammatory conditions 4

Important distinction: Normal ESR should prompt serious reconsideration of the diagnosis, as values are almost never normal in acute rheumatic fever except in isolated chorea. 7

5. Additional Laboratory Tests

• Complete blood count - may show leukocytosis and anemia of chronic disease 4
• Electrocardiogram - prolonged PR interval is a minor criterion 1
• Throat culture or rapid streptococcal antigen test - though often negative by the time rheumatic fever develops 3

Diagnostic Algorithm

1. Suspect acute rheumatic fever based on clinical presentation (arthritis, carditis symptoms, chorea, rash, nodules)
2. Obtain streptococcal serology (ASO titer, additional antibodies if needed) 4
3. Measure acute phase reactants (ESR, CRP) 4
4. Perform standard echocardiography with Doppler in all cases, regardless of auscultation findings 1, 6
5. Obtain ECG to assess for PR prolongation 1
6. Apply Jones Criteria based on risk stratification of the population 1, 5

Common Pitfalls to Avoid

• Do not rely on cardiac auscultation alone - echocardiography is mandatory as it detects subclinical carditis missed by clinical examination 1
• Do not diagnose without documented streptococcal infection - except in rare cases of isolated chorea or indolent carditis 1, 3
• Do not use outdated Jones Criteria - the 2015 revision includes critical changes including subclinical carditis and risk stratification 1, 5
• Do not overlook monoarthritis in high-risk populations - this is now accepted as a major criterion in moderate-to-high-risk areas 1, 5

Histopathologic Confirmation

While Aschoff bodies with Anitschkow cells on histology confirm active acute rheumatic carditis, modern diagnosis relies on clinical criteria and echocardiography rather than histologic confirmation. 2 Surgical valve specimens may incidentally reveal Aschoff bodies, warranting intensified secondary prophylaxis. 2