Anti-Streptolysin O Antibody (ASO) Blood Test
The anti-streptolysin O antibody (ASO) blood test is generally used to help confirm if a recent strep infection with group A streptococcus:
- Is the source of glomerulonephritis, a type of kidney disease
- Is the root of rheumatic fever in an individual with signs and symptoms
This test may be ordered on its own or together with the anti-DNase B test which is also used to detect recent strep infections.
In most cases, antibiotics are used to identify and treat strep infections and resolve infections. However, complications (sequelae), namely rheumatic fever and glomerulonephritis, may develop in some people, especially young children, in cases where they do not cause identifiable symptoms and/or go untreated. Therefore, the test is ordered if a person has symptoms of rheumatic fever or glomerulonephritis and has a recent history of sore throat or a confirmed streptococcal infection. When the symptoms appear, it is ordered, usually in the weeks after a sore throat or skin infection when the bacteria are no longer present in the throat or on the skin.
Rheumatic fever produces symptoms that may include:
- Skin Rash
- Pain in more than one joint and joint swelling, especially in the elbows, wrists, ankles, and knees, sometimes moving from one joint to another
- Rapid, jerky movements (Sydenham’s chorea)
- Sometimes the heart can become inflamed (carditis); this may not produce any symptoms but also may lead to shortness of breath, heart palpitations, or chest pain
- Small, painless nodules under the skin
Glomerulonephritis produce symptoms that may include:
- High blood pressure
- Fatigue, decreased energy
- Swelling (edema)
- Decreased urine output
- Joint pain
- Bloody urine
However, in other conditions, these symptoms can be seen.
The test can be performed twice for acute and convalescent ASO titers, with samples collected about two weeks apart. This is done to determine whether the level of the antibody rises, drops or remains the same.
Using certain antibiotics and corticosteroids can decrease the level of ASO antibodies.
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