Is a throat swab or a blood test used to diagnose strep throat?
Strep throat is usually investigated with a swab for a rapid antigen test or culture; molecular tests may also be available. Blood antibody tests reflect a response to earlier infection and do not alone diagnose acute strep throat or determine current antibiotic need.
Details
Why symptoms may not be enough
Viral and streptococcal infections can share symptoms. Without clear viral features, a clinician may need a swab to guide treatment. A red throat alone does not establish a need for antibiotics.
If the rapid test is negative
US guidance generally recommends a backup culture after a negative rapid antigen test in symptomatic children aged three or older. This is not routinely required in adults. The next step depends on the test type, age and clinical assessment; ask how and when results will be communicated.
What raised antibodies mean
An antistreptolysin O titre can remain elevated after the infection has resolved. It may help investigate certain complications alongside history, examination and other tests, but does not alone prove rheumatic fever. Do not begin or repeat antibiotics solely because an antibody result is high.
Related reading: Does a child need antibiotics for a cold or green mucus?.