At-Risk Youth Medicaid Protection Act of 2018 This bill prohibits a state Medicaid program from terminating a juvenile's medical assistance eligibility because the juvenile is incarcerated. A state may suspend coverage while the juvenile is an inmate, but must reevaluate the juvenile's eligibility prior to the juvenile's release (without requiring a new application) and, if appropriate, restore coverage upon release. A state must also process an application submitted by, or on behalf of, an incarcerated juvenile in a manner that ensures the juvenile's eligibility is determined upon release. A "juvenile" is an individual who: (1) is under 21 years of age; or (2) has aged out of the state's foster care system, was enrolled in the state plan while in foster care, and is under 26 years of age.