Your doctor tests for strep throat with a rapid antigen test. The doctor swabs the back of your throat with a cotton-tipped stick to get a sample. You usually get results in about 20 minutes. If the test is negative (meaning no signs of strep are found), the doctor may do what’s called a throat culture. He or she will take more swab samples from the back of your throat and send them to a lab. You may have to wait a couple of days for those results.