Antistreptolysin O (ASO, ASLO) Titer Blood Test

Antistreptolysin O (ASO, also known as ASLO or AST) is a blood test that measures the level of antibodies against streptolysin O — a toxin produced by group A beta-hemolytic streptococcus (Streptococcus pyogenes). These antibodies appear in the body after a streptococcal infection.

This test helps determine whether you’ve had a recent streptococcal infection. It’s especially useful in cases where the infection itself has passed, but complications have begun — such as inflammation of the joints, kidneys, or heart.

The ASO test may be recommended if: ✦ there's suspicion of acute rheumatic fever,

• you’ve had a post-streptococcal glomerulonephritis (kidney inflammation),
• or you have skin-related issues such as erysipelas, peeling, scarlet fever, or a psoriasis flare-up.

In some cases, the test is performed after skin trauma (e.g. an injury to the leg) to rule out a hidden streptococcal infection.

🔍 Optimal ASO levels

• ASO levels below 200 IU/mL are generally considered normal for adults.
• In children, normal ranges may be lower and depend on age and laboratory standards.

🔷 Elevated ASO levels

A positive or elevated ASO titer suggests a recent streptococcal infection. This might have been a silent infection in the throat or skin that still triggered the immune system.

• A rise in ASO is a diagnostic clue in cases of rheumatic fever or post-streptococcal kidney inflammation.
• High ASO levels can persist for several months and don’t always mean treatment is required, especially if no other symptoms are present.

🩺 Possible symptoms and conditions associated with high ASO:

• Joint inflammation (arthritis)
• Kidney inflammation (glomerulonephritis)
• Erysipelas (a skin infection)
• Postpartum fever
• Complications like endocarditis (heart), osteomyelitis (bones), or meningitis (brain)

🍽 What to do if your result is high?

• If symptoms are present, your doctor may prescribe antibiotics — usually penicillin — to reduce the risk of complications.
• In cases like kidney or joint inflammation, antibiotics may be needed long-term, sometimes for several years.
• Severe infections affecting the heart, bones, or brain require hospitalization and medical supervision.

🩹 When to see a doctor?

If your ASO test was ordered by a physician or if you’re experiencing symptoms that may be related to a recent streptococcal infection, it’s essential to discuss your results with your doctor. Only they can determine whether treatment is needed and assess the immune response.

🛑 If you have acute symptoms — fever, joint pain, swelling, skin rash, changes in urination or consciousness — seek medical help immediately.