The anti-streptolysin O (ASO) antibody can indicate a recent or ongoing strep infection, which can lead to serious complications. Testing for ASO levels can help diagnose strep-related diseases such as rheumatic fever, scarlet fever, and heart or kidney infections. Elevated ASO levels do not necessarily mean an active infection and further testing may be needed.
Anti-streptolysin O (ASO) is an antibody often found in the blood of people who have had a strep infection. A blood test, known as an anti-streptolysin O titer, is sometimes used to check for this antibody in the blood. This test is considered useful because some health conditions, such as rheumatic fever, usually only occur in people who have recently had or are suffering from a strep infection. Although testing for anti-streptolysin O is not considered effective in diagnosing a specific disease, it can help doctors determine whether a patient has a strep-related disease.
People who have had a strep infection within the past few months may still have the antibody to streptolysin O in their blood. People who have an active strep infection may also have the antibody in their blood. Common strep infections can include strep throat, rheumatic fever, scarlet fever, and bacterial endocarditis.
Strep infections can cause serious complications, including inflammation of the membrane surrounding the heart. Streptococcal bacteria can also cause serious kidney infections. Rheumatic fever and scarlet fever are considered severe forms of strep infection.
Testing for these antibodies with an antistreptolysin O titer can help doctors diagnose a patient’s symptoms. If the test indicates that a strep infection has occurred, doctors may be able to better diagnose scarlet fever, rheumatic fever, or an infection of the heart or kidneys. Some conditions, such as rheumatoid arthritis, can cause symptoms similar to those of a strep infection, but usually do not occur due to this infection.
The levels of anti-streptolysin O antibodies in the blood are measured by taking a small sample of blood, usually from a vein in the hand or arm. Normal blood levels of antistreptolysin O usually do not exceed 160 units per milliliter of blood. When a person has high ASO levels, doctors may consider the possibility of an ongoing strep infection. However, high blood levels of ASO do not necessarily mean that the infection is still present. They could mean that the person has recently suffered from a strep infection but has recovered in the last few months.
If elevated ASO levels are found in the blood and symptoms of continuing disease are present, further diagnostic tests may be needed. Doctors typically tailor treatment for strep infection based on the patient’s specific illness and individual needs.
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