Finding the right tests…
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Finding the right tests…
Microbiology
A throat swab culture grows a sample taken from the back of your throat to check for group A streptococcus, the bacteria behind strep throat, along with other bacteria that can cause a sore throat. Most clinics now use a rapid antigen test first, since it gives a quick answer, but the rapid test misses some real infections. When the rapid test is negative and your doctor still suspects strep, especially in a child or teenager, a culture is sent as well, since untreated strep throat in that age group carries a risk of rheumatic fever that adults don't share to the same degree.
This test reports whether group A streptococcus, or another disease-causing bacteria, grows from a swab of your throat and tonsils. It's more accurate than the rapid antigen test that's usually done first, catching some genuine infections the rapid test misses, which is why a negative rapid test in a child or teenager is often backed up with a culture rather than accepted on its own. A positive result confirms bacterial strep throat, supporting a decision to treat with antibiotics rather than let a sore throat run its course untreated.
A rapid strep test gives an answer within minutes by detecting a protein on the bacteria's surface, but it can miss real infections that a culture would catch, since it depends on there being enough bacteria on the swab to trigger a positive result. A culture, which actually grows whatever bacteria are present, is more sensitive.
Adults with a negative rapid test are often not cultured further, since strep throat in adulthood carries little risk beyond the sore throat itself. Children and teenagers are different: untreated strep throat in that age group can lead to rheumatic fever weeks later, a preventable complication that affects the heart, which is why doctors are more cautious about accepting a negative rapid test at face value in this group.
The swab is rubbed onto growth plates and incubated. If group A streptococcus or another disease-causing bacteria is present, it multiplies into colonies that a lab technician can identify, a process that takes meaningfully longer than the few minutes a rapid test needs, since real growth has to happen first.
A normal or negative culture means no bacteria that cause sore throat were found, pointing toward a viral cause that antibiotics won't help. An abnormal or positive result identifies the bacteria responsible, which is what supports starting antibiotic treatment.
A rapid test gives a fast answer but can miss some real infections. If it's negative but your doctor still suspects strep, especially in a child or teenager, a culture is sent to check more thoroughly.
It can trigger a brief gagging feeling as the swab touches the back of your throat and tonsils, but the swab itself takes only a few seconds. It isn't painful in the way an injection or blood draw is.
Untreated strep throat in children and teenagers can lead to rheumatic fever weeks later, a complication that can damage the heart. Adults face much lower risk of this complication, which is part of why testing is more cautious in younger patients.
This page is general information about the test, not medical advice. Your own report's reference ranges apply — please discuss your results with your doctor.
Avoid antiseptic mouthwash right before the swab, since it can interfere with detecting bacteria on the sample. Ask your doctor or the centre about any other preparation.
It means no strep or other sore-throat-causing bacteria were found, which points toward a viral cause. Antibiotics won't help a viral sore throat, so your doctor will usually recommend supportive care instead.
A positive culture for group A streptococcus is usually treated with antibiotics, partly to prevent complications like rheumatic fever. Your doctor makes the final call based on your symptoms and health history.