From the Guidelines
A Streptococcal A titer greater than 30.0 indicates a significant immune response to Group A Streptococcus bacteria, suggesting either a current or recent streptococcal infection. This elevated level is typically seen in patients who have been infected with Strep A, which can cause conditions like strep throat, scarlet fever, or more serious complications such as rheumatic fever or post-streptococcal glomerulonephritis. The most recent and highest quality study, 1, provides guidance on the diagnosis and management of Group A Streptococcal pharyngitis. If you have symptoms like sore throat, fever, or rash, treatment with antibiotics such as penicillin (500 mg orally twice daily for 10 days) or amoxicillin (500 mg orally three times daily for 10 days) is typically recommended, as outlined in 1. For those allergic to penicillin, alternatives include azithromycin (500 mg on day 1, then 250 mg daily for 4 more days) or clindamycin (300 mg orally three times daily for 10 days), as stated in 1. Complete the full course of antibiotics even if symptoms improve quickly to prevent complications. The elevated titer reflects antibodies your immune system has produced against streptococcal antigens, and these levels may remain high for weeks to months after the infection has cleared, as discussed in 1. It is essential to note that antistreptococcal antibody titers reflect past and not present immunologic events and therefore cannot be used to determine whether an individual with pharyngitis and GAS in the pharynx is truly infected or merely a streptococcal carrier, as mentioned in 1. However, when present, elevated or rising antistreptococcal antibody titers provide reliable confirmation of a recent GAS infection and are of value in identifying a preceding GAS infection in a patient suspected of having rheumatic fever, as stated in 1.
From the Research
Streptococcal Antibody Titer
- A Streptococcal (Group A Streptococcus) antibody titer greater than 30.0 may indicate a recent or past infection with Group A Streptococcus 2.
- The diagnosis of streptococcal infection is typically made by testing for multiple antibodies, including ASO, ASK, and ADN-B, and if two or more of these titers are positive, it can indicate a fairly recent streptococcal infection 2.
- However, if only one of these titers is positive, it may indicate a previous or non-specific infection 2.
- The normal values for ASO and anti-DNase B titers vary by age, and for children ages 2 to 12 in the United States, the upper limit of normal (ULN) for ASO is 240 and for anti-DNase B is 640 3.
- Elevated antibody levels, including ASO and anti-DNase B, can persist for extended periods in patients with rheumatic valvular disease, and may be involved in the pathogenesis or be an outcome of the valvular disease 4.
Clinical Interpretation
- The clinical interpretation of a Streptococcal antibody titer greater than 30.0 should take into account the patient's medical history, symptoms, and other laboratory results 5, 2.
- A high antibody titer may indicate a recent or ongoing infection, while a low titer may indicate a past infection or no infection at all 2.
- The use of rapid streptococcal antigen tests and throat cultures can also aid in the diagnosis of streptococcal infections 5.
Laboratory Results
- Laboratory results, including antibody titers and throat culture results, should be interpreted in the context of the patient's clinical presentation and medical history 5, 2.
- The results of these tests can help guide treatment decisions and determine the need for further testing or follow-up care 5, 2.