Hello, Chickenpox causes a red, itchy skin rash that usually appears first on the abdomen or back and face, and then spreads to almost everywhere else on the body, including the scalp, mouth, arms, legs, and genitals The chickenpox vaccine is 99% effective at preventing the VZV infection in kids. Doctors recommend that kids receive the chickenpox vaccine twice. Chicken is detected by characteristics rashes . No need of lab test.