Throat Culture and Strep Testing: Understanding Your Report

Section Editor: Rodney E. Rohde PhD
June 3, 2026

Most sore throats are caused by viruses and get better on their own. Testing for strep throat is done to determine whether a sore throat is caused by a bacterium called group A Streptococcus (often abbreviated as group A strep). This matters because strep throat can be treated with antibiotics, while a viral sore throat cannot. A bacterium is a microorganism, a living thing too small to see without a microscope, and an antibiotic is a medicine used to treat infections caused by bacteria.

This article explains the tests used to check for strep throat, including the rapid strep test, the throat culture, and newer molecular tests, and what the wording on your report means, so you can better understand a report you have received.

What is strep throat, and why test for it?

Group A strep is the most common bacterial cause of a sore throat, an illness doctors call pharyngitis (inflammation of the throat). Most sore throats, however, are caused by viruses. Testing helps distinguish a strep infection from a viral one, so antibiotics are used only when they will help.

Finding strep matters because treating it can shorten the illness, lower the chance of spreading it to others, and reduce the small risk of complications. These complications include rheumatic fever, which can affect the heart, and a kidney problem called glomerulonephritis. Because most sore throats are viral, and because some healthy people carry the bacteria without being sick (explained later), doctors usually decide whether to test based on your symptoms rather than testing every sore throat.

The rapid strep test (an antigen test)

The rapid strep test, sometimes called a rapid antigen detection test, looks for antigens (pieces) of group A strep on a swab rubbed against the back of the throat. It gives a result within minutes. Like other antigen tests, described in the article on PCR, antigen, and antibody tests, how much you can rely on the result depends on which way it comes out:

A positive result is usually trustworthy — Antigens of group A strep were found, which points to strep throat, and treatment usually follows.
A negative result is less certain — The rapid test can miss some infections. In children and teenagers, who have a higher chance of strep and of its complications, a negative rapid test is often confirmed with a throat culture. In adults, a negative rapid test is often accepted without a culture, because strep and its complications are less common.

Throat culture

The throat culture is the traditional and most reliable test. The swab is spread on a culture plate and kept warm so that any bacteria present can grow, usually over one to two days. The laboratory specifically looks for group A strep because the throat normally contains many harmless bacteria, called normal flora. Because throat culture is more sensitive than the rapid test, it is the most commonly used test to confirm a negative rapid test result, especially in children.

Molecular (PCR) tests

Newer molecular tests, also called nucleic acid amplification tests, look directly for the genetic material of group A strep, as explained in the article on PCR, antigen, and antibody tests. They are fast, often yielding results in minutes to about an hour, and they are both very sensitive and very specific. Because they are so accurate, a negative molecular test may not need to be confirmed by culture, and these tests are increasingly used in place of older methods.

How to read your result

The wording on your report depends on which test was done.

Rapid strep test positive — Antigens of group A strep were found, pointing to strep throat. This result is usually reliable.
Rapid strep test negative — No antigens were found. In children, this is often confirmed with a throat culture, because the rapid test can miss some infections.
Throat culture: group A streptococcus isolated — The bacteria grew, confirming strep throat.
Throat culture: no group A streptococcus, or normal flora — Group A strep did not grow. The sore throat is likely caused by something else, most often a virus.
Molecular test: detected or not detected — The genetic material of group A strep was, or was not, found.

Strep carriers and antibiotic testing

Some people, especially children, carry group A strep in the throat without being sick. This is called being a carrier. In a carrier, a positive test may reflect the carried bacteria rather than the cause of a current sore throat, which is another reason your doctor weighs the test result against your symptoms.

Unlike urine and blood cultures, a throat culture for strep usually does not include antibiotic susceptibility testing. This is because group A strep reliably responds to standard antibiotics such as penicillin, so the laboratory does not need to test which antibiotics will work. Susceptibility to alternative antibiotics may be assessed for people allergic to penicillin. There is also a separate blood test called the antistreptolysin O (ASO) test, which looks for antibodies to strep. It is not used to diagnose a current sore throat; instead, it can help when a complication of a past strep infection is suspected.

What happens after these tests

Strep testing indicates whether group A strep is present and informs the decisions you and your healthcare team make together, rather than dictating them on its own.

If the test is positive, strep throat is usually treated with antibiotics to shorten the illness, reduce the risk of spreading it, and lower the small risk of complications; it’s important to finish the full course as directed. If the test is negative, strep is unlikely, and a viral sore throat is managed with supportive care such as rest, fluids, and pain relief, since antibiotics would not help. In children, a negative rapid test may be followed by a throat culture before a final decision is made.

Questions to ask your doctor

Which test did I (or my child) have, a rapid strep test, a throat culture, or a molecular test?
Does my result mean my sore throat is caused by strep or by a virus?
If the rapid test was negative, should it be confirmed with a throat culture?
Could a positive result mean I am a carrier rather than having an active infection?
If I have strep, which antibiotic do you recommend, and for how long?
I am allergic to penicillin. Will my strep need susceptibility testing for another antibiotic?
How long am I contagious, and when can I return to school or work?
What symptoms would mean I need to come back?
Why are antibiotics not recommended if my test is negative?
Who should I contact if my symptoms get worse?