Streptococci and ASO titer

• Streptococci are gram-positive bacteria
• have several immunologic groups named by letters A-H and K-O
• produce enzymes
• group C, G, and A produce the same enzyme, streptolysin O
• an oxygen-labile hemolytic toxin, mainly cause hemolysis of the red blood cells
• When the body is infected with one of the above groups (C, G, or A), it produces antibodies to the streptolysin O toxin, called antistreptolysin O or ASO
• ASO titer measures these antibodies in the blood serum
• antibodies level starts to rise in 1-3 weeks after streptococcal infection, peaks in 3-5 weeks, and then goes back to insignificant level over 6-12 months, so a positive test can indicate current but more recent group A, C, and G streptococcal infection and may support the diagnosis of post-streptococcal infection complication (bacterial endocarditis, glomerulonephritis, rheumatic fever, pediatric autoimmune neuropsychiatric disorders associated with streptococcus (PANDAS)]
• ASO titers may be negative in up to 20% of patients who develop acute rheumatic fever
• Rising titers over time are more indicative of infection than a single test (repeating the test is recommended 10 days after the initial test)
• It is important to keep in mind that too many people are exposed to these bacteria without being symptomatic, thus the presence of ASO by itself does not indicate the disease, but a titer of more than 166 Todd units (>200 IU) in general is considered a definite elevation and positive ASO test in adults
• Increased titer can occur in healthy carrier
• Limitations:
• Antibiotics may give false negative results by inhibiting streptococcal antibody response, while increased Beta-lipoprotein levels, liver disease, and tuberculosis may give false positive results. Repeating test in 10 days is recommended
• Another test like anti-DNase B (anti-deoxyribonuclease B) should be considered, which, when combined with the ASO titer, can detect up to 95% of streptococcal infections compared to 80% with the ASO titer test alone.

Streptococci are a group of bacteria belonging to the genus Streptococcus, which are gram-positive, facultative anaerobes, and typically form chains or pairs of cocci. Some species of streptococci are part of the normal flora of the human body and are found in the respiratory, gastrointestinal, and genitourinary tracts. However, certain species can cause a range of infections, including strep throat, scarlet fever, pneumonia, and invasive diseases such as sepsis and meningitis.

One important test related to streptococcal infections is the Antistreptolysin O (ASO) titer. ASO is an antibody produced by the immune system in response to infection with group A Streptococcus (Streptococcus pyogenes). The ASO titer test measures the level of ASO antibodies in the blood and is used to diagnose recent or past streptococcal infections, particularly those involving the throat (such as strep throat) or rheumatic fever.

Here's how the ASO titer test works and its clinical significance:

1. Test Procedure:

   • Blood is drawn from the patient, usually from a vein in the arm.
   • The blood sample is then sent to a laboratory for analysis.
   • In the laboratory, the level of ASO antibodies in the blood is measured using various methods, such as enzyme-linked immunosorbent assay (ELISA) or nephelometry.

2. Interpretation:

   • Normal ASO titers vary depending on the laboratory and the population being tested. However, significantly elevated ASO titers suggest recent or past streptococcal infection.
   • Rising ASO titers over time may indicate an active or ongoing streptococcal infection, while declining titers may suggest resolution of the infection.
   • ASO titers are often interpreted in conjunction with clinical symptoms and other laboratory tests to diagnose streptococcal infections, monitor treatment response, and assess the risk of complications such as rheumatic fever.

3. Clinical Significance:

   • Elevated ASO titers are most commonly associated with group A Streptococcus infections, particularly strep throat and rheumatic fever.
   • The ASO titer test is useful in diagnosing recent streptococcal infections, especially when throat culture results are negative or inconclusive.
   • It is also used to assess the risk of developing rheumatic fever, a serious inflammatory condition that can occur following untreated or inadequately treated streptococcal infections.

In summary, the ASO titer test is a valuable tool in the diagnosis and management of streptococcal infections, particularly those caused by group A Streptococcus. It helps healthcare providers identify recent infections, guide treatment decisions, and assess the risk of complications such as rheumatic fever.

References:

• DELMAR'S Guide to Laboratory and Diagnostic Tests. 2nd Edition. 2010.
• J. MH Danchin, JB Carlin,W Devenish, TM Nolan and JR Carapetis. Paediatr. New normal ranges of antistreptolysin O and antideoxyribonuclease B titres for Australian children. Child Health. 2005. 41:583–586.
• Manual of Laboratory & Diagnostic Tests.
• Hilário MO, Terreri MT. Rheumatic fever and post-streptococcal arthritis. Best Pract Res Clin Rheumatol. 2002 Jul. 16(3):481-94. [Medline].
• Datta G. Syncope in a child. Ann Pediatr Cardiol. 2013 Jan. 6(1):93-4