From the Guidelines
A blood test is not the preferred method for diagnosing strep throat, and instead, a rapid antigen detection test and/or culture of a throat swab should be used. According to the IDSA guidelines updated in 2013 1, diagnosis of group A streptococcal pharyngitis should be confirmed using a rapid antigen detection test and/or culture of a throat swab. The key points to consider are:
- A positive result on rapid antigen detection testing is diagnostic for group A streptococcal pharyngitis
- A backup culture should be performed in children and adolescents with negative test results
- A backup culture is generally not necessary in adults because the incidence of the illness and the risk of subsequent rheumatic fever are low in adults Some blood tests, like a complete blood count, might show elevated white blood cells during a strep infection, but this is nonspecific and not diagnostic. Antibody tests like ASO (anti-streptolysin O) are sometimes used to detect previous strep infections when investigating complications like rheumatic fever, but they're not useful for diagnosing acute strep throat, as stated in the guidelines 1.
From the Research
Blood Test for Strep
- The diagnosis of streptococcal pharyngitis can be made using throat culture or rapid strep test, with throat culture being the diagnostic standard 2.
- Rapid antigen detection testing has improved significantly in terms of sensitivity and specificity, and can be used to identify streptococcal pharyngitis, especially in patients with severe symptoms or special situations that warrant early detection 3.
- The modified Centor score can be used to help physicians decide which patients need no testing, throat culture/rapid antigen detection testing, or empiric antibiotic therapy 3, 4.
- A blood test is not typically used to diagnose streptococcal pharyngitis, as the infection is usually localized to the throat and can be diagnosed using throat culture or rapid strep test 2, 3, 5.
- However, some studies have investigated the use of rapid strep tests in the diagnosis of streptococcal pharyngitis, and have found that these tests can be useful in reducing unnecessary antibiotic prescriptions 6.
Diagnostic Tests
- Throat culture is considered the diagnostic standard for streptococcal pharyngitis, but rapid antigen detection testing has improved significantly in terms of sensitivity and specificity 2, 3.
- Rapid strep tests can be used to identify streptococcal pharyngitis, especially in patients with severe symptoms or special situations that warrant early detection 2, 3.
- The modified Centor score can be used to help physicians decide which patients need no testing, throat culture/rapid antigen detection testing, or empiric antibiotic therapy 3, 4.
Treatment
- Penicillin and amoxicillin are first-line antibiotics for the treatment of streptococcal pharyngitis, with a recommended course of 10 days 3, 5.
- First-generation cephalosporins are recommended for patients with nonanaphylactic allergies to penicillin 3, 5.
- Steroids are not recommended for symptomatic treatment of streptococcal pharyngitis 5.