Antistreptolysin O titre

Antistreptolysin O Titre

The Antistreptolysin O (ASO) titre is a blood test that measures the presence of antibodies against streptolysin O, a toxin produced by group A Streptococcus bacteria. This test is primarily used to help diagnose a past infection with these bacteria, which can lead to conditions such as rheumatic fever and post-streptococcal glomerulonephritis.

Background

Streptolysin O is an exotoxin produced by group A Streptococcus, which is responsible for diseases such as strep throat, scarlet fever, and skin infections. When the body is infected with these bacteria, it produces antibodies to fight off the infection. The ASO titre measures the level of these antibodies in the blood.

Clinical Significance

The ASO titre is particularly useful in diagnosing conditions that occur after a streptococcal infection. For instance, rheumatic fever is an inflammatory disease that can develop after an untreated or inadequately treated strep throat or scarlet fever. Similarly, post-streptococcal glomerulonephritis is a kidney disease that can occur after a streptococcal skin or throat infection.

A high ASO titre indicates a recent streptococcal infection, as the antibody levels typically rise 1 to 3 weeks after the infection and peak at about 3 to 5 weeks. The levels then gradually decrease but can remain elevated for several months.

Test Procedure

The ASO titre test is a simple blood test. A healthcare provider will draw a blood sample from a vein, usually in the arm. The sample is then sent to a laboratory where it is analyzed for the presence and concentration of antistreptolysin O antibodies.

Interpretation of Results

- Normal Range: The normal range for ASO titres can vary depending on the laboratory, but generally, a titre of less than 200 units/mL is considered normal in adults, while in children, a titre of less than 150 units/mL is typical. - Elevated ASO Titre: An elevated ASO titre suggests a recent streptococcal infection. However, it is important to note that not all individuals with a streptococcal infection will have an elevated ASO titre, and some individuals may have elevated titres without any symptoms of infection.

Limitations

The ASO titre test has limitations. It does not indicate the presence of an active infection, only that an infection has occurred in the past. Additionally, it does not identify the specific type of streptococcal infection or its location in the body.

Also see

• Streptococcal infection
• Rheumatic fever
• Post-streptococcal glomerulonephritis
• Streptolysin O
• Antibody