ASO Titre Test
If your doctor has ordered an ASO titre test, you likely have a history of sore throat or symptoms that suggest a complication from a strep infection. This blood test measures antibodies your immune system made against streptolysin O, a toxin produced by Group A Streptococcus bacteria. It does not diagnose a current sore throat — instead, it helps your doctor determine whether a past strep infection may have triggered conditions like rheumatic fever or kidney inflammation.
What Is an ASO Titre Test?
The ASO (anti-streptolysin O) titre test detects antibodies your body produces in response to Group A Streptococcus (GAS) bacteria. After an infection such as strep throat or scarlet fever, your immune system creates these antibodies, which typically appear 1–3 weeks later and peak at 4–6 weeks. The test measures the level of these antibodies in your blood. A high titre indicates a recent or past infection, but it cannot tell your doctor if the infection is still active.
Why Is the ASO Titre Test Ordered?
Doctors order this test when they suspect a post-streptococcal complication. Common reasons include:
- Suspected acute rheumatic fever (especially in children with joint pain, heart murmur, or skin nodules)
- Post-streptococcal glomerulonephritis (kidney inflammation after strep infection)
- Unexplained joint pain or swelling
- Follow-up after a documented strep infection to check for antibody response
- Evaluating a heart murmur that may be due to rheumatic heart disease
In Bangladesh, where rheumatic heart disease remains common, this test is frequently used to support clinical diagnosis.
How to Prepare for the Test
No special preparation is needed. The test involves a simple blood draw from a vein in your arm. You do not need to fast. However, timing matters: the antibodies take time to rise. If the test is done too early after a sore throat (within the first week), it may be falsely negative. Doctors often order a second test 2–4 weeks later to see if the titre is rising.
Understanding Your ASO Titre Results
Normal reference ranges vary by laboratory. In general:
- Adults: <200 IU/mL
- Children: <150 IU/mL
Always compare your result with the reference range provided on your lab report.
The table below explains common result patterns.
| Result Pattern | What It May Indicate | Clinical Context |
|---|---|---|
| Normal (low titre) | No recent GAS infection | Unlikely to have post-streptococcal complication |
| Single high titre (e.g., >200 IU/mL) | Recent GAS infection (within weeks to months) | Supports diagnosis of post-streptococcal complication if symptoms are present |
| Rising titre between two samples (2–4 weeks apart) | Active or recent infection | Stronger evidence of recent GAS infection; often used to confirm rheumatic fever |
Note: A single high titre alone is not diagnostic. Doctors use the Jones criteria (major and minor manifestations) to diagnose acute rheumatic fever. The ASO titre is just one piece of evidence.
What Are the Limitations of the ASO Titre Test?
This test has important limitations:
- It cannot diagnose a current strep throat infection. Antibodies take weeks to rise, so a negative test does not rule out an active infection.
- Up to 20% of healthy individuals may have mildly elevated titres without any symptoms (false positive).
- It does not distinguish between a new infection and an old one unless paired samples show a rise.
- For some patients, especially with skin infections (impetigo), the anti-DNase B test may be more useful.
- The test is not recommended for routine screening of strep throat.
Cost of ASO Titre Test in Bangladesh
The test is widely available in diagnostic centers across Bangladesh. Prices vary by location, lab quality, and whether you order a single test or paired tests.
| Item | Approx. BDT Range | Notes |
|---|---|---|
| ASO Titre Test (single) | 300–500 ৳ | Common in city labs; may be higher in private hospitals |
| ASO Titre Test (paired, two samples) | 600–800 ৳ | Some labs offer package for two tests |
| Anti-DNase B test (if needed) | 500–1,000 ৳ | Often ordered alongside ASO for skin infections |
Prices are indicative and may change. Confirm with your chosen lab before testing.
Find a Doctor in Your Division
If your ASO titre result is abnormal or you have symptoms suggestive of rheumatic fever or kidney disease, consult a qualified doctor. Use the table below to find medicine specialists (or pulmonologists) in your division.
| Division | Find a doctor |
|---|---|
| Dhaka | Medicine Specialists in Dhaka |
| Chattogram | Medicine Specialists in Chattogram |
| Khulna | Medicine Specialists in Khulna |
| Rajshahi | Medicine Specialists in Rajshahi |
| Rangpur | Medicine Specialists in Rangpur |
| Sylhet | Medicine Specialists in Sylhet |
| Barishal | Medicine Specialists in Barishal |
| Mymensingh | Pulmonologists in Mymensingh |
When Should You See a Doctor?
You should consult a doctor if:
- Your ASO titre is significantly elevated
- You have joint pain, swelling, or redness
- You experience chest pain, palpitations, or shortness of breath
- You notice dark, foamy urine or swelling in your legs (possible kidney involvement)
- You have a history of strep throat and develop new symptoms
A rheumatologist, pediatrician, or general physician can evaluate your condition. The ASO titre test is a tool — it does not replace a thorough clinical examination.
Key Takeaways
- The ASO titre test detects past Group A streptococcal infection, not current infection.
- It is used to support diagnosis of rheumatic fever and post-streptococcal glomerulonephritis.
- Interpretation requires clinical correlation; a single high titre is not enough.
- Normal ranges vary; always check your lab’s reference.
- In Bangladesh, cost is around 300–800 BDT.
- Consult a doctor for proper evaluation.
Frequently Asked Questions
How long after a sore throat should I take the ASO titre test?
The ASO titre test is not for detecting an active sore throat. If a complication is suspected, the test is usually done 2 to 4 weeks after the throat infection, because antibody levels start rising around 1 week and peak at 4 to 6 weeks. Testing too early may give a false negative. Your doctor will decide the best timing based on your symptoms.
Can my ASO titre be high even if I never had a noticeable sore throat?
Yes. Some people carry Group A Streptococcus without obvious throat symptoms (asymptomatic infection), yet their immune system still produces antibodies. A high ASO titre in such cases may still be relevant if you have unexplained joint pain, rash, or kidney issues. However, a raised titre alone does not confirm a complication — your doctor will correlate it with your symptoms and other tests.
What does a normal ASO titre mean? Does it rule out a past strep infection?
A normal ASO titre suggests that you likely have not had a recent Group A strep infection in the past few months. However, it does not completely rule out a past infection — if the infection was very mild or if the test was done too early or too late, the antibody level may not be elevated. Also, some people produce a weak antibody response. Your doctor will consider the result together with your clinical history.
Is any special preparation needed before the ASO titre blood test?
No special preparation like fasting is required for the ASO titre test. However, tell your doctor about any medications you are taking, as certain antibiotics or immunosuppressive drugs may affect antibody production. The test is a simple blood draw from a vein, and you can eat and drink normally beforehand.
If my ASO titre result is high, what happens next?
A high ASO titre alone is not a diagnosis. Your doctor will review your symptoms (such as joint swelling, chest pain, or dark urine) and may order additional tests — for example, an ECG or echocardiogram for heart involvement, or a urine test to check for kidney inflammation. Depending on the findings, you may be referred to a rheumatologist, cardiologist, or nephrologist. Do not start any treatment (including antibiotics) based solely on the titre result.
Sources
The following sources are from international journals, government health agencies, or recognized medical organizations:
- Streptococcal Antibody Tests – StatPearls (NCBI) (ncbi.nlm.nih.gov)
- Rheumatic Heart Disease – World Health Organization (who.int)
- World Health Organization — ASO Titre Test (who.int)
- MedlinePlus — ASO Titre Test (medlineplus.gov)
- CDC — ASO Titre Test (cdc.gov)
- NHS — ASO Titre Test (nhs.uk)