Why is Anti-streptolysin O (ASO) High? Causes, Symptoms, and What to Do

Anti-streptolysin O (ASO) is an antibody that your body produces in response to an infection by group A Streptococcus bacteria. A high ASO level can be a sign that your body is reacting to a recent streptococcal infection. This article will explore what causes elevated ASO levels, the symptoms you might experience, and when it might be time to talk to your doctor.

What is Anti-streptolysin O (ASO)?

Anti-streptolysin O (ASO) is an antibody that the immune system produces when it detects streptolysin O, a toxin released by group A Streptococcus bacteria. These bacteria are responsible for infections such as strep throat and skin infections. The ASO test measures the level of these antibodies in the blood, which can help determine if there has been a recent streptococcal infection.

Why ASO Levels Matter

ASO levels are important because they can indicate a past infection with group A Streptococcus, which is not always apparent through symptoms alone. Typically, ASO levels in adults are less than 200 IU/mL. A high ASO level can be evidence of a recent infection, which is crucial for diagnosing conditions like rheumatic fever or post-streptococcal glomerulonephritis (a type of kidney inflammation). However, it is not used to diagnose an active infection like a sore throat.

Causes of High ASO Levels

A high ASO level typically results from a recent group A Streptococcus infection. These infections can include:

• Strep throat: A common infection characterized by a sore throat, fever, and swollen lymph nodes.
• Scarlet fever: A condition that can occur after strep throat, marked by a red rash and high fever.
• Skin infections: Such as impetigo, although after skin infections ASO often rises only weakly, so doctors may use other strep antibody tests instead.

The ASO test is often used to support the diagnosis of complications that can follow these infections, such as rheumatic fever and post-streptococcal glomerulonephritis.

Symptoms Associated with High ASO Levels

While high ASO levels themselves do not cause symptoms, they are associated with conditions resulting from group A Streptococcus infections. Symptoms of these conditions may include:

• Joint pain and swelling
• Fever
• Fatigue
• Red, swollen skin rashes
• Tea-colored urine (indicative of kidney issues)

Frequently asked questions

What does a high ASO level mean?

A high ASO level means that there has been a recent infection with group A Streptococcus bacteria. It suggests that the body has reacted to this infection, but it does not indicate an active infection.

Can high ASO levels be treated?

High ASO levels themselves do not require treatment. However, if they are associated with conditions like rheumatic fever, those conditions will need medical attention and appropriate treatment.

How long do ASO levels remain elevated?

ASO levels can remain elevated for weeks to months following a streptococcal infection. The duration can vary depending on individual health factors and the nature of the infection.

When to see a doctor

If you have symptoms that may indicate a complication of a streptococcal infection, such as persistent joint pain, skin rashes, or changes in urine color, it is important to consult a healthcare provider. They can determine whether further testing is needed and discuss appropriate treatment options.

Remember, while a high ASO level can provide valuable information about past infections, it is not used to diagnose an active infection. Any decisions regarding your health should be made in consultation with your healthcare provider.