According to the Centers for Disease Control and Prevention (CDC), bats, skunks, raccoons, and foxes that bite humans should be euthanized and tested as soon as possible.
In order to do the test, the animal must be euthanized and tissue samples are taken from the brain. In the United States, rabies test results are usually ready within 24 to 72 hours from the time after the animal is euthanized. (The test itself takes two hours, but the sample must be sent to a diagnostic laboratory.)
Not all animals that bite or scratch a human are euthanized and tested. Animals that are considered to be less likely to have rabies (such as a healthy, vaccinated domestic cat or dog) may be observed for 10 days.