anti streptolysin o (aso / aslo) Test

ASO titer

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what is an antistreptolysin o titer test?

An Antistreptolysin O test is a blood test that helps to measure the antibodies produced by the body in response to a toxin known as Streptolysin O. Our body produces antibodies in order to defend itself when it comes in contact with any harmful bacteria.

These antibodies are customized to fight against the particular kind of bacteria it encounters and the aso titre test measures these antibodies. The aso titer test is helpful in determining if you have been affected by a strep infection in the recent past.

It is often performed to confirm streptococcal infection, kidney disorders and rheumatic fevers.

why is the aso titer test conducted?

Your doctor may order the aso test to be conducted if he notices symptoms related to an earlier infection due to Group A streptococcus. The antistreptolysin antibodies can remain the system up to 3 to 8 weeks after a strep infection and levels can be high for several months.

By conducting this test, the doctor will determine if a post-streptococcal complication causes the aso titre symptoms. The bacteria can cause the following illness:

  • Strep throat
  • Scarlet fever
  • Bacterial endocarditis which infects the inner lining of the heart
  • Glomerulonephritis, a kidney infection
  • Rheumatic fever which impacts bones, joints and even the heart

how should one prepare for an aso test?

The test includes drawing a blood sample from the veins, and you may receive some instructions of do’s and don’ts before the test. You will have to refrain from consuming food or water about six hours before the test.

Inform your doctor about any medications that you are currently taking, including prescribed and OTC drugs. Your doctor will also ask you to stop taking medications like certain antibiotics and corticosteroids.

The doctor could find it difficult to arrive at the right diagnosis as these medications could influence the aso result.

are there any complications associated with the aso titer test?

Most people wonder what is aso test and are there any major complications that this test could cause?

Fortunately, the risks involved are minimal though a slight pain may be experienced while blood is being drawn or after the blood is drawn. A few other risks with aso are as follows:

  • Infection at the puncture point
  • Excess bleeding where the needle is pricked
  • Multiple punctures if difficulty in locating the vein
  • Hematoma (blood accumulation under the skin)
  • Fainting in certain cases

If you notice any kind of swelling or blood flow from the puncture site, bring it to the notice of your doctor immediately for a quick resolution.

what does the aso report indicate?

The aso titer normal range is one below 200 in case of adults while an ASO test value below 100 is considered normal for kids below age 5. However, results may slightly vary from lab to lab and your doctor will consider this before suggesting aso titre treatment for any complications.

Any post-streptococcal complication will be indicated by an elevated ASO value. If the aso report is negative but is inconclusive for the doctor to arrive at a diagnosis, you may have to carry out an additional antibody test. The titer test cost will vary from city to city so check before you carry out the test.

The test may have to be repeated after two weeks in order to confirm the diagnosis since ASO antibodies are produced with a week of the infection. As a thumb rule, increasing antibodies indicates that the infection is recent while decreasing antibodies show that the infection is reducing.

Understanding results ofAnti Streptolysin O (ASO / ASLO)

Reference RangeInterpretation
Below 200 IU/mlNegative

Inference: If a false negative is suspected, then an anti-DNase B titre should be sought. False positives can result from liver disease and tuberculosis.

‘*A Reference range is a set of values which helps the healthcare professional to interpret a medical test. It may vary with age, gender, and other factors. Reference ranges may also vary between labs, in value & units depending on instruments used and method of establishment of reference ranges’


With all the above information, it should now be clear what is aso. Do not be worried if the normal values vary slightly and speak to your doctor to clear your doubts. Also, ask him to explain the meaning of the test results for complete peace of mind.