Detecting rabies in humans before symptoms appear is very difficult. Blood tests alone cannot reliably diagnose rabies, because the virus hides within nerve tissue rather than circulating in the blood. Doctors use specialized tests on saliva, cerebrospinal fluid (CSF), or skin biopsies from the back of the neck to detect viral RNA or antibodies. These methods, such as PCR (polymerase chain reaction) and fluorescent antibody testing, can confirm infection — but they’re usually effective only after symptoms begin. That’s why rabies is treated based on exposure risk, not waiting for test results, since early vaccination is the only way to prevent the disease.