Final answer:
The social worker should first perform a mental status exam to assess the client's cognitive and psychological state as a foundational step before considering other interventions.
Step-by-step explanation:
If a social worker notes that a client frequently shifts the conversation to completely unrelated topics while obtaining a psycho-social history, the social worker should first perform a mental status exam. This initial step is crucial in understanding and documenting the client's current cognitive state which includes orientation, memory, language, sensorium, and judgment and abstract reasoning abilities. Before considering other steps such as conferring about medication, scheduling family therapy, or referring for cognitive testing, the mental status exam provides a baseline for identifying any immediate cognitive or psychological concerns that might need to be addressed within the outpatient clinic setting.