What is Anti Streptolysin O/ ASO titre - Quantitative?
Also Known As:
Antistreptolysin O Titer
Antistreptolysin O (ASO) is an antibody targeted against streptolysin O, a toxic enzyme produced by group A Streptococcus bacteria. ASO and anti-DNase B are the most common of several antibodies that are produced by the body’s immune system in response to a strep infection with group A Streptococcus. This test measures the amount of ASO in the blood.
Group A Streptococcus (Streptococcus pyogenes) is the bacterium responsible for causing strep throat and a variety of other infections, including skin infections (pyoderma, impetigo, cellulitis). In most cases, strep infections are identified and treated with antibiotics, and the infections resolve.
When a strep infection does not cause identifiable symptoms, goes untreated, or is treated ineffectively, however, complications, namely rheumatic fever and a type of kidney disease (glomerulonephritis), can sometimes develop, especially in young children. These secondary conditions have become much less prevalent in the U.S. because of routine strep testing, but they still do occur. These conditions can cause serious complications such as heart damage, acute kidney dysfunction, tissue swelling (edema), and high blood pressure (hypertension). The ASO test can be used to help determine if these are due to a recent group A strep infection.
How is the test used?
The ASO test is primarily used to help determine whether a recent strep infection with group A Streptococcus:
- Is the cause of a person’s or glomerulonephritis, a form of kidney disease
- Caused rheumatic fever in a person with signs and symptoms
The test may be ordered by itself or along with an anti-DNase B, another test used to detect recent strep infections.
In most cases, strep infections are identified and treated with antibiotics and the infections resolve. In cases where they do not cause identifiable symptoms and/or go untreated, however, complications can develop in some people, especially young children. The test, therefore, is ordered if a person presents with symptoms suggesting rheumatic fever or glomerulonephritis and has had a recent history of sore throat or confirmed streptococcal infection.
Since the incidence of post-streptococcal complications has dropped in the U.S., so has the use of the ASO test.
When is it ordered?
The ASO test is ordered when a person has symptoms that a health practitioner suspects may be due to an illness caused by a previous strep infection. It is ordered when the symptoms emerge, usually in the weeks following a sore throat or skin infection when the bacteria are no longer present in the throat or on the skin.
Some symptoms of rheumatic fever may include:
- Joint swelling and pain in more than one joint, especially in the ankles, knees, elbows and wrists, sometimes moving from one joint to another
- Small, painless nodules under the skin
- Rapid, jerky movements (Sydenham’s chorea)
- Skin rash
- 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
Some symptoms of glomerulonephritis may include:
- Fatigue, decreased energy
- Decreased amount of urine
- Bloody urine
- Joint pain
- Swelling (edema)
- High blood pressure
However, these symptoms can be seen in other conditions.
The test may be performed twice, with samples collected about two weeks apart, for acute and convalescent ASO titers. This is done to determine if the antibody level is rising, falling, or remaining the same.