In an asymptomatic patient with a markedly elevated antistreptolysin‑O (ASO) titre of 666 IU/mL and normal renal function, is any further work‑up required?

Management of Elevated ASO Titre in an Asymptomatic Patient with Normal Renal Function

In an asymptomatic patient with an ASO titre of 666 IU/mL and normal kidney function, no further work-up is required unless there are clinical signs or symptoms suggesting post-streptococcal complications such as acute rheumatic fever or post-streptococcal glomerulonephritis. 1

Understanding ASO Titre Elevation

An elevated ASO titre in an asymptomatic patient reflects a previous streptococcal infection, not an active disease process requiring intervention. 1, 2

• ASO titres begin rising approximately 1 week after streptococcal infection and peak between 3-6 weeks, then can remain elevated for several months even after uncomplicated infections. 1, 2
• The upper limit of normal varies significantly by age and geographic location—ranging from 239 IU/mL to 515 IU/mL in different pediatric populations. 3, 4
• Your patient's titre of 666 IU/mL, while elevated, falls within the range commonly seen in healthy school-age children in some populations (up to 1:320 or approximately 640 IU/mL). 5

When ASO Testing is Actually Indicated

ASO testing should ONLY be ordered to confirm previous streptococcal infection in patients with suspected post-streptococcal complications—it is not a screening test for asymptomatic individuals. 1, 2

The American Heart Association recommends ASO testing specifically for:

• Acute rheumatic fever: Patients presenting with migratory arthritis, carditis, chorea, erythema marginatum, or subcutaneous nodules. 1
• Post-streptococcal glomerulonephritis: Patients with hematuria, proteinuria, edema, and hypertension. 1, 6

Critical Clinical Assessment

Since your patient is asymptomatic with normal renal function, evaluate for any subtle signs of post-streptococcal complications:

Rule Out Acute Rheumatic Fever

Look for:

• Migratory polyarthritis or arthralgia 1
• Any cardiac symptoms (chest pain, palpitations, dyspnea) 1
• Involuntary movements (Sydenham's chorea) 1
• Skin manifestations (erythema marginatum, subcutaneous nodules) 1

Rule Out Post-Streptococcal Glomerulonephritis

Verify:

• Absence of hematuria (microscopic or gross) 6
• No edema or recent weight gain 6
• Normal blood pressure 6
• Confirmed normal renal function (you've already done this) 6

What NOT to Do

Common pitfalls to avoid:

• Do not prescribe antibiotics based solely on an elevated ASO titre—treatment is warranted only when acute rheumatic fever or post-streptococcal glomerulonephritis is confirmed. 1
• Do not order serial ASO measurements in asymptomatic patients, as titres remain elevated for months and trending adds no clinical value. 1, 2
• Do not confuse elevated ASO with active infection—ASO cannot distinguish between active infection and chronic carriage with intercurrent viral illness. 2
• Do not use ASO to diagnose acute pharyngitis—rapid antigen detection test or throat culture are the appropriate tests for acute infection. 2

When Further Work-Up IS Indicated

Proceed with additional testing only if the patient develops:

• Inflammatory markers elevation: Check ESR and CRP if any symptoms develop, as these should be elevated in true post-streptococcal complications. 1
• Cardiac evaluation: ECG (to assess PR interval) and echocardiogram (to detect valve lesions) are mandatory if any signs of carditis emerge. 1
• Complement levels: Low C3 with normal C4 supports post-streptococcal glomerulonephritis if renal symptoms develop. 6

Practical Recommendation

For your asymptomatic patient with ASO 666 IU/mL and normal kidneys:

• Reassure the patient that this represents a past streptococcal exposure, not active disease. 1, 2
• No antibiotics, no serial testing, no specialist referral needed at this time. 1
• Advise the patient to return if symptoms of arthritis, cardiac issues, or urinary changes develop. 1
• Document the elevated ASO in the chart as baseline for future reference if post-streptococcal complications arise later. 1

The key principle is that laboratory abnormalities without clinical disease do not warrant treatment or further investigation—this applies universally to elevated ASO titres in asymptomatic individuals. 1, 7