Which investigations should be ordered to evaluate for post‑streptococcal complications such as rheumatic fever, glomerulonephritis, and deep neck space infection?

Investigations for Post-Streptococcal Complications

Order acute phase reactants (ESR and CRP), antistreptococcal antibody titers (ASO and anti-DNase B), urinalysis, ECG, and echocardiography to evaluate for rheumatic fever and glomerulonephritis following strep throat.

Core Laboratory Tests

Confirming Recent Streptococcal Infection

• Antistreptococcal antibody titers are essential for documenting recent group A streptococcal infection 1
  • Antistreptolysin O (ASO): Rises at 1 week, peaks at 3-6 weeks post-infection
  • Anti-DNase B: Rises at 1-2 weeks, peaks at 6-8 weeks post-infection
  • If ASO is not elevated, obtain anti-DNase B as it may be positive when ASO is not 1
  • Critical caveat: Normal levels are higher in school-age children than adults—misinterpretation is common 1

Acute Phase Reactants

• ESR and CRP are mandatory for detecting inflammation 2, 3, 4
  • CRP must exceed the upper limit of normal for the laboratory
  • Use peak ESR values as they evolve during acute rheumatic fever 2
  • These are part of the minor Jones criteria for rheumatic fever diagnosis

Cardiac Evaluation for Rheumatic Fever

Electrocardiography

• ECG is essential to detect PR interval prolongation (first-degree AV block), which represents a minor Jones criterion 2, 3

Echocardiography

• Echocardiography is recommended to identify both clinical and subclinical carditis 2, 3
  • Can detect valvulitis (mitral or aortic regurgitation) that qualifies as a major Jones criterion
  • Subclinical carditis detected only by echo can now be considered in diagnosis 2
  • In acute rheumatic fever, only the coapting portion of the anterior mitral leaflet tip prolapses—this differs from myxomatous prolapse 2

Renal Evaluation for Glomerulonephritis

Urinalysis

• Urinalysis with microscopy to detect hematuria (microscopic or gross), proteinuria, and RBC casts 3, 5, 6
  • Post-streptococcal glomerulonephritis presents with a spectrum from asymptomatic microscopic hematuria to gross hematuria with edema and hypertension 3

Additional Renal Tests

• Serum creatinine to assess kidney function 7, 5
• Complement levels (C3) are typically low in post-streptococcal glomerulonephritis and help differentiate from other causes 5, 6

Diagnostic Algorithm for Rheumatic Fever

The revised Jones criteria require 2:

• Evidence of recent streptococcal infection (positive ASO/anti-DNase B) PLUS
• Two major criteria OR one major + two minor criteria

Major criteria: Carditis/valvulitis, polyarthritis, chorea, erythema marginatum, subcutaneous nodules

Minor criteria: Fever, arthralgia, elevated ESR/CRP, prolonged PR interval on ECG

Imaging for Deep Neck Space Infections

If deep neck space infection is suspected (severe throat pain, neck swelling, trismus, dysphagia):

• CT scan with contrast is the imaging modality of choice 8, 9
  • Used in 85.3% of cases to identify location, extent, and character (cellulitis vs abscess) 8
  • Essential for surgical planning if drainage is needed

Common Pitfalls to Avoid

• Don't rely on throat culture alone for post-streptococcal complications—antibody titers are needed to confirm recent infection 1
• Don't miss subclinical carditis—echocardiography may be the only way to detect it 2
• Don't misinterpret normal pediatric antibody levels as pathologic—children have higher baseline titers than adults 1
• Don't forget that both rheumatic fever and glomerulonephritis can occur simultaneously in the same patient, though rare 7