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Anti-Streptolysin O Antibody ASO

Also known as Streptolysin-O Antibody, ASO Streptococcus, ASO test, Anti-streptolysin O Titer

What is an anti-streptolysin O antibody (ASO) Test?

An anti-streptolysin O antibody (ASO) is a blood test that determines if you've had a recent infection caused by group A streptococcus bacteria. The test doesn't diagnose a current strep infection, such as strep throat. Instead, this test is mainly ordered if your doctor suspects that your present symptoms might be due to an infection that you have had recently but left untreated.

What is the test used for?

The anti-streptolysin O antibody test measures antibodies produced by your body in reaction to a toxin known as streptolysin O. If you have a strep infection caused by GAS bacteria, your body makes the anti-streptolysin O antibodies. 

Why and when do you need an ASO Test?

Usually, the doctor will prescribe antibiotics to clear it up when you come under the influence of strep bacteria and have an infection. But sometimes, people don't have significant symptoms, so they don't know they need treatment. This you may develop secondary complications. You may need an ASO titer blood test if your health care provider suspects you have one of the following complications.

Infection: Infections. Without proper treatment, strep bacteria can flare to other areas of your body. It can cause infections in your tonsils, sinuses, skin, middle ear, and blood.

Scarlet fever: It is most prevalent in children between the ages of five and fifteen. Previously, people used to consider Scarlet fever as a severe childhood ailment. Now antibiotics can treat the disease effectively and reduce the potential risks. However, if left untreated, the disease can cause severe damage. Symptoms include:

  • Red rash that seems like a sunburn and feels like sandpaper
  • Red lines near the groin, armpits, elbows, knees, and neck
  • Flushed face with a pale ring around the mouth
  • A red and rough tongue that may be covered with a white coating.

Rheumatic fever: Rheumatic fever is not an infection but an inflammatory immune response. It is not contagious, and in doctors' opinion, it might be your body's immune reaction to a previous strep or scarlet fever infection. Rheumatic fever is a severe condition involving your heart, joints, brain, and skin. The signs and symptoms of rheumatic fever can include: 

  • Fever
  • Pain and tenderness in joints of knees, wrist, and arms
  • Chest pain
  • Shortness of breath
  • Tiredness
  • Uncontrollable jerking
  • Though it's rare, you may find lumps under the skin
  • Rarely, a rash of pink rings with a clear center. 

Glomerulonephritis. It is a type of kidney disease. It injures the small filters inside your kidneys called glomeruli. It can cause your kidneys to have problems clearing waste and fluid from your body. Severe cases can lead to kidney failure. Sometimes glomerulonephritis does not show any symptoms. If you notice any of these signs, talk to your doctor.

  • Blood in the urine
  • Tiredness
  • Nausea
  • Rash
  • High blood pressure
  • Pain in your joints or abdomen
  • Peeing less or more than usual
  • Foamy urine
  •  Swelling in your face or joints

What kind of sample is required for the test?

For an ASO titer test, you need to give a sample of your blood. A nurse or phlebotomist will withdraw a blood sample from a vein in your hand or arm. They will tie a wristband around your hand or arm to prominent the vein. Then a needle will be used to enter your vein and draw your blood into a tube. The sample will be sent to the lab for assessment.

Do you need to prepare for the test?

Ask your healthcare provider for any preparations before the test. You may need to withhold from eating or drinking anything for six hours before the test. Your doctor might ask you to stop taking some medications before this test. For instance, corticosteroids and certain antibiotics may decrease anti-streptolysin O antibody levels, affecting your test results. Ensure that your doctor knows about all the medicines you have been taking, including prescription and over-the-counter drugs. However, don't withhold medication without your physician's consent.

Are there any risks to this test?

Like with any blood test, the risks are minimal. You may feel slight pain or bruise in the puncture site.

Other risks of withdrawing a blood sample include:

  • Difficulty in taking a sample which may cause multiple pricks and discomfort.
  • Excessive bleeding
  • Fainting due to blood loss
  • Accumulation of blood under the skin, known as a hematoma
  • Infection at the needle site

What do the test results mean?

Generally, an ASO test value below 200 is considered normal for adults. Various factors may affect your test results, including age, gender, health history, and testing methods. Sometimes test results do not indicate a problem, no matter higher or lower than normal ranges. It's better to discuss the results with your healthcare provider to understand what they mean.

Negative Result:

A negative result indicates that you don't have antibodies against strep infection in your blood. Because antibodies take time to increase in the blood after infection, so your doctor may advise you to repeat the ASO titer test after two weeks of your first blood sample. 

Positive Result:

A positive result means that antibodies are present in your blood. It indicates that you have had a strep infection recently. However, sometimes an anti-streptolysin test won't show an increase in antibodies in conditions such as rheumatic fever. Your doctor may advise further tests to evaluate the disease in such cases. 

Some Other Tests With ASO Include:

If you visit your doctor with strep throat, he might order a quick streptococcal antigen test or a throat culture to detect GAS bacteria. Similarly, if the doctor suspects an infection in other parts of the body, he will advise you to get other cultures done of your blood, tissues, or mucus in your lungs. If your healthcare provider suspects you have rheumatic fever, he will order other antibodies tests. Some antibodies that might be present in your blood are anti-DNAse B, anti-hyaluronidase, or anti-streptozyme. These tests can assist your doctor in deciding if you have rheumatic fever.

Our clinical experts continually monitor the health and medical content posted on CURA4U, and we update our blogs and articles when new information becomes available. Last reviewed by Dr. Saad Zia on August 15 th, 2023.

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