You are eligible to take the Missouri nurse aide exam if you were trained as a nursing assistant in the long-term care unit of a hospital, and if you have been working there as a nurse assistant for a minimum of twelve months. Individuals trained in acute care units of hospitals as nurse assistants or as psychiatric aides must meet special criteria to challenge the CNA examination. They need to attend an orientation class focusing on geriatric residents' needs; they also need to complete one hundred hours of on-the-job training in a long-term care facility or long-term care unit of a hospital.