Group A beta-hemolytic streptococci are associated with streptococcal infections or illness.

These tests detect antibodies to enzymes produced by organisms. Group A beta-hemolytic streptococci produce several enzymes, including streptolysin O, hyaluronidase, and DNase B. Serologic tests that detect these enzyme antibodies include antistreptolysin O (ASO) titer, which detects streptolysin O; streptozyme, which detects antibodies to multiple enzymes; and anti-deoxyribonuclease B (ADB) titer, which detects DNase B. Serologic detection of streptococcal antibodies helps to establish prior infection but is of no value for diagnosing acute streptococcal infections. Acute infections should be diagnosed by direct streptococcal cultures or the presence of streptococcal antigens.

The ASO titer test aids in the diagnosis of several conditions associated with streptococcal infections, such as rheumatic fever, glomerulonephritis, bacterial endocarditis, and scarlet fever. Serial rising titers over several weeks are more significant than a single result. ADB antibodies may appear earlier than ASO in streptococcal pharyngitis, and this test is more sensitive for streptococcal pyoderma.

• ASO titer:

  • Adult: <160 Todd units/mL or <200 IU

  • Child (5–12 years of age): 170–330 Todd units/mL or <100 IU

• ADB titer: A negative test is normal

  • Preschool-age children: <60 Todd units/mL

  • School-age children: <170 Todd units/mL

  • Adults: <85 Todd units/mL

• Streptozyme: Negative for streptococcal antibodies

1. Collect a 7-mL blood serum sample in a red-topped tube. Observe standard precautions. Label the specimen with the patient’s name, date, and tests ordered and place in a biohazard bag for transport to the laboratory.

2. Repeat testing is recommended 10 days after the first test.

1. In general, a titer >160 Todd units/mL is considered a definite elevation for the ASO titer test.

2. The ASO or the ADB titer test alone is positive in 80%–85% of group A streptococcal infections (e.g., streptococcal pharyngitis, rheumatic fever, pyoderma, glomerulonephritis).

3. When ASO and ADB titer tests are run concurrently, 95% of streptococcal infections can be detected.

4. A repeatedly low titer is good evidence for the absence of active rheumatic fever. Conversely, a high titer does not necessarily mean rheumatic fever of glomerulonephritis is present; however, it does indicate the presence of a streptococcal infection.

5. ASO titer production is especially high in rheumatic fever and glomerulonephritis. These conditions show marked ASO titer increases during the symptomless period preceding an attack. Also, ADB titers are particularly high in pyoderma.

Pretest Patient Care

1. Assess patient’s clinical history and test knowledge. Explain test purpose and procedure.

2. Follow guidelines in Chapter 1 for safe, effective, informed pretest care.

1. An increased titer can occur in healthy carriers.

2. Antibiotic therapy suppresses streptococcal antibody response.

3. Increased B-lipoprotein levels inhibit streptolysin O and produce falsely high ASO titers.