Antistreptolysin O titer (ASO)

What sample is needed for the Antistreptolysin O titer (ASO)?

1. The test is performed on the patient’s serum (clotted blood, 3-5 mL).
2. A random sample can be taken.
3. Avoid hemolysis.

What are the Indications for the Antistreptolysin O titer (ASO)?

1. To diagnose exposure to Streptococcal infection.
2. To diagnose poststreptococcal diseases, such as:
   1. Glomerulonephritis.
   2. Rheumatic fever.
   3. Bacterial Endocarditis.
   4. Scarlet fever.
3. A significant level was seen in glomerulonephritis and rheumatic fever.

What are the precautions for the Antistreptolysin O titer (ASO)?

1. Avoid the drug-like steroids and antibiotics that decrease the ASO titer.
2. Increased beta-lipoprotein inhibits streptolysin O and gives a falsely high ASO titer.
3. Early injection of penicillin prevents the rise of the titer.

What are the complications of Streptococcus group A?

1. Lancefield group A streptococci are also known as Streptococcus pyogenes.
2. Group A β-streptococci produce various infections; the most common is acute pharyngitis.
3. It can produce scarlet fever, erysipelas, vesicular cellulitis, and puerperal fever.
4. There are a few reports showing conditions like staphylococcal toxic shock syndrome.

What enzymes are produced by the Beta-hemolytic Streptococci group A?

1. Beta-hemolytic group A streptococci produce many enzymes that can contribute to their pathogenicity. Two of these are:

2. Streptolysin O:

   1. O stands for oxygen-labile, as it is inactivated by oxygen.
   2. Streptolysin O is produced after 7 to 10 days of the infection, and antibodies start to appear.
   3. At the end of 2 months, only 70% to 75% of the tests are positive.
   4. At 6 months, 35% of the cases are positive.
   5. At 12 months, 20% are positive.

1. 1. What are the functions of Streptolysin O?
   2. Streptolysin O enzyme destroys the red blood cells and white blood cells.
   3. This is why it is called β-hemolytic group A streptococci and exhibits beta-hemolytic activity.
   4. This enzyme is antigenic.
   5. Patients develop an anti-streptolysin O (ASO) antibody.
   6. The highest level of ASO titer occurs during the third week of infection for acute rheumatic fever.
   7. At this stage, positivity is 80% to 85%, and antibodies start declining later.

2. Streptolysin S:

   1. The “S” stands for oxygen stable.
   2. This can cause beta hemolysis.
   3. This is not antigenic.

How will you determine Antistreptolysin O (ASO)?

1. ASO is measured by the latex agglutination or haemagglutination procedure.
2. This test measures antibodies against Streptolysin O, an antigen produced by Group A beta-hemolytic streptococci.
3. RBCs are added as an indicator system.

4. The ASO antibody may be detected in the blood weeks or months after the infection has resolved.

What are the important facts about Beta-Streptococci?

1. Group A-beta streptococci can be isolated from throat or nasopharynx culture in 15% to 20% (range 11% to 60%) of normal children.
2. Taking two swabs instead of one will increase the likelihood of a positive culture result.
   1. Group A streptococci are always sensitive to penicillin, as confirmed by in vitro sensitivity testing.
3. Streptolysin O is an extracellular toxin produced by many of the streptococci groups, particularly by group A β-hemolytic streptococci.
   1. Streptolysin O has the ability to destroy the red blood cells (hemolysis).
   2. The Streptolysin O enzyme is antigenic, and the immune system produces antibodies, such as the Antistreptolysin O antibody (ASO).

When is the time of the appearance of ASO and SO?

1. SO is antigenic, and it produces an antibody against the SO antigen.
2. ASO appears in the serum approximately one week to one month after a streptococcal infection.
   1. This ASO is a neutralizing antibody.
3. ASO has no value for the diagnosis of acute streptococcal infection.
4. The rising serial titer of ASO over weeks, followed by a gradual decline in titer, is more significant for streptococcal infections.
   1. After 6 months, only 30% of the patients show abnormal titer.
5. The highest level of ASO is seen in glomerulonephritis and rheumatic fever.
   1. A fourfold rise in the titer is significant for acute and convalescent patients.
   2. The 500 to 5000 Todd units/mL level suggests acute post-streptococcal glomerulonephritis, rheumatic fever, or acute poststreptococcal endocarditis.
   3. 15% of the active Rheumatic fever patients show a test negative.

What is the procedure for the Antistreptolysin O titer (ASO) antibody titer?

What is the interpretation of the ASO titer?

1. The rising titer is more significant than a single test.
2. It is positive when it is >250 IU. Positive levels are from 400 to 5000 IU.
3. ASO, even in streptococcal infections, is elevated in 70% to 80% of patients.
4. The raised level of the ASO is not related to the severity of the disease, and the fall is also unrelated to the disease’s course.
5. Approximately 30% to 40% of patients with streptococcal pyoderma exhibit elevated ASO levels.
6. 50% of patients show raised ASO levels in glomerulonephritis, and 20% is seen in membranous glomerulonephritis.

What is the value of Antistreptolysin O (ASO) titer in various diseases?

Where will you see False-positive results?

1. Patients with tuberculosis.
2. Liver diseases like active viral hepatitis.
3. Bacterial contamination.
4. The latex agglutination test may yield a false-positive result in samples with lipemia or contamination.

What is the normal antistreptolysin O (ASO)?

Source 2

• Adult / elderly =>160 Todd unit/mL or <200 IU.
  • 6 months to 2 years = ≤50 Todd units/mL.
  • 2 to 4 years = ≤ 160 Todd units /mL
  • 5 to 12 years  = 170 to 330 Todd units/mL.
• If it is >200 Todd units, then it is a significant level; it suggests recent or relatively recent group A streptococcal infection.
• A greater than 500 Todd units indicates acute rheumatic fever or acute post-streptococcal glomerulonephritis.
• Serial assay of ASO should be advised for rising titer.

What direct evidence of antistreptococcal antibodies indicates?

1. Streptococcal pharyngitis and tonsillitis.
2. Scarlet fever.
3. Erysipelas.

What is the indirect evidence of ASO for the diagnosis of?

1. Rheumatic fever.
2. Differential diagnosis of joint pains of rheumatoid arthritis and rheumatic fever.
3. Detection of the subclinical streptococcal infection.
4. Glomerulonephritis.

What is the relation between Streptococcal infections and ASO titer?

1. An ASO titer raised above the baseline indicates recent group A streptococcus pharyngitis within the last 2 months.
2. The increased titer develops 7 to 14 days after infection and rises rapidly to a peak within 4 to 6 weeks.
3. Then it declines in the next 4 to 6 months.

1. Bacterial Endocarditis.
2. Post-streptococcal glomerulonephritis (50% to 70 % of the patients show no high titer).
3. Rheumatic fever.
4. Scarlet fever.
5. Streptococcal pyoderma.
   1. ASO is often not raised in these diseases.

What is important for the ASO titer?

1. An increased titer may be found in the healthy carrier.
2. Antibiotic therapy may suppress the antibody response.
3. Increased Lipoprotein levels inhibit Streptolysin O and produce a falsely high ASO titer.

Questions and answers: