ASO Titers & Anti-DNase B: When They Matter, When They Don't, and the Jones Criteria Refresher

 

ASO Titers & Anti-DNase B: When They Matter, When They Don't, and the Jones Criteria Refresher

Stop ordering ASO for every sore throat. It's only relevant when you suspect a post-streptococcal complication—not for diagnosing acute pharyngitis.

What ASO and Anti-DNase B Measure

Both are antibodies against Group A Streptococcus (GAS) antigens. They indicate prior streptococcal infection—not current infection. They peak 3–6 weeks after the strep infection and decline over months.

• ASO (Anti-Streptolysin O): Rises after pharyngeal GAS infection. Peaks at 3–5 weeks. More sensitive for post-pharyngitis complications (ARF, PSGN).
• Anti-DNase B: Rises after both pharyngeal AND skin GAS infections. Peaks at 6–8 weeks. More sensitive for post-skin-infection complications (especially PSGN after impetigo). Stays elevated longer than ASO.

The #1 Misuse

ASO should NOT be ordered to diagnose acute strep pharyngitis. The rapid strep test and throat culture are the tests for acute GAS. ASO is only useful when you suspect a post-streptococcal complication (ARF, PSGN, PANDAS) and need evidence of prior strep infection.

When to Order

• Suspected Acute Rheumatic Fever (ARF): Child with migratory polyarthritis, carditis (new murmur), chorea, erythema marginatum, or subcutaneous nodules 2–4 weeks after pharyngitis. ASO + anti-DNase B together provide the best sensitivity (~95% combined).
• Suspected Post-Streptococcal Glomerulonephritis (PSGN): Child with cola-colored urine, edema, hypertension 1–3 weeks after pharyngitis or 3–6 weeks after skin infection. Low C3 is the hallmark. ASO (pharyngeal) or anti-DNase B (skin) confirms recent strep.
• PANDAS/PANS evaluation: Controversial, but some clinicians check ASO/anti-DNase B in acute-onset OCD or tics following strep infection.

The Jones Criteria (2015 Updated)

ARF requires evidence of prior GAS infection (positive ASO/anti-DNase B, positive throat culture, or positive rapid strep) PLUS:

• Low-risk populations: 2 major criteria, OR 1 major + 2 minor criteria
• Moderate/high-risk populations: Same, but with expanded definitions (e.g., monoarthritis and lower fever thresholds qualify)

Major criteria: carditis, polyarthritis (or monoarthritis in high-risk), chorea, erythema marginatum, subcutaneous nodules. Minor criteria: fever, polyarthralgia (or monoarthralgia in high-risk), elevated ESR/CRP, prolonged PR interval.

Interpretation Pitfalls

• Elevated ASO alone doesn't mean anything pathologic: Up to 15–20% of school-age children have elevated ASO at any time from recent subclinical strep exposure. It must be interpreted in clinical context.
• A single ASO level is less useful than paired titers: A rising titer (4-fold increase between acute and convalescent specimens 2–4 weeks apart) is stronger evidence of recent infection than a single elevated level.
• ASO may be negative after skin infections: Streptolysin O is inactivated by skin lipids. For post-impetigo PSGN, anti-DNase B is more sensitive.
• Age-specific norms: Children normally have higher ASO levels than adults due to frequent strep exposure. Use age-appropriate reference ranges (>200 IU/mL is generally considered elevated in children; >160 in adults).
• Rheumatic heart disease without acute findings: In endemic areas, echocardiographic screening may detect subclinical rheumatic heart disease without a history of ARF. ASO may be normal by this point.

The PSGN Lab Pattern

This connects to the complement and urinalysis posts in this series:

• Low C3 (consumed via alternative pathway) with normal C4—the classic complement pattern for PSGN
• Urinalysis: Hematuria (dysmorphic RBCs, RBC casts), proteinuria
• Elevated ASO or anti-DNase B: Confirms recent strep
• C3 normalizes within 6–8 weeks. If C3 remains low beyond 8–12 weeks, suspect a different glomerulonephritis (lupus nephritis, MPGN, C3 glomerulopathy).

Bottom Line

ASO and anti-DNase B prove prior strep infection—they don't diagnose acute pharyngitis. Order them for suspected ARF or PSGN, not for sore throats. Use both together for best sensitivity. And remember: ASO is better for post-pharyngeal complications, anti-DNase B is better for post-skin-infection complications.

Stay sharp out there.