A nurse in an emergency department is caring for a client who has a closed head injury. Which of the following actions should the nurse take first?

A. Preparing the client for an MRI is not the first step; assessment of neurological status is the priority. B. Inserting an indwelling urinary catheter is unnecessary unless indicated after further assessment. C. Determining the Glasgow Coma Scale score is the most important initial step to assess the client's neurological status and guide further interventions. D. Administering mannitol is appropriate for increased intracranial pressure but should only be done after assessing the client's neurological condition.