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Antistreptolysin O Titer (ASO) - ASO

What does the Antistreptolysin O Titer (ASO) - ASO blood test mean? Get a free analysis of your blood test now. Here's what you get with our free analysis:

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The Antistreptolysin O Titer (ASO) test measures antibodies produced by the immune system in response to a streptococcal infection. It's primarily used to diagnose and monitor conditions like rheumatic fever or post-streptococcal glomerulonephritis, which can occur after a strep throat infection. The test detects antibodies against streptolysin O, a toxin produced by group A Streptococcus bacteria. A rising or elevated ASO titer suggests a recent or ongoing streptococcal infection. However, the test is not used to diagnose acute strep throat, as it takes several weeks for ASO levels to rise after infection. It's most useful in identifying post-streptococcal complications or confirming a recent streptococcal infection when symptoms are unclear.

Acceptable Range:   0 to 200
Ideal for Women:   <200
Ideal for Men:   <200
Ideal for Girls:   <200
Ideal for Boys:   <200
Test Method: This test is typically performed on a blood sample.

What do readings below 0 IU/mL for Antistreptolysin O Titer (ASO) - ASO mean?

A low ASO titer (below the range lower) is generally not a cause for concern. It typically indicates that there has not been a recent streptococcal infection or that the body has not produced a significant antibody response to such an infection. This could mean:

  1. The individual has not been recently infected with group A Streptococcus.
  2. The immune system has not mounted a strong antibody response to a streptococcal infection.
  3. The infection occurred too recently for antibodies to have developed.
  4. The individual may have a compromised immune system that doesn’t produce adequate antibodies.

A low result does not rule out the possibility of a current streptococcal infection, as it takes time for antibodies to develop.

What do readings above 200 IU/mL for Antistreptolysin O Titer (ASO) - ASO mean?

A high ASO titer (above the range upper) typically indicates a recent or current infection with group A Streptococcus bacteria. This elevated level suggests that the body has produced a significant amount of antibodies in response to the infection. A high ASO titer may indicate:

  1. A recent strep throat infection (usually within the past 2-4 weeks).
  2. The presence of post-streptococcal complications such as rheumatic fever or glomerulonephritis.
  3. A chronic or recurring streptococcal infection.
  4. In some cases, it may be a false positive due to cross-reactivity with other antibodies.

It’s important to note that ASO levels can remain elevated for several months after an infection, so clinical correlation is necessary for proper interpretation.

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