Final answer:
The social worker should first perform a mental status exam to assess the client's cognitive functions before considering further steps.
Step-by-step explanation:
When a social worker notes that a client frequently shifts the conversation to completely unrelated topics, the first step they should take is to perform a mental status exam. This will help assess the client's cognitive functions such as memory, orientation, language, and thinking. If during the conversation and interactions with the client, the social worker notices cognitive or language deficits, they could pursue this in more depth to understand the potential underlying issues. A mental status exam includes tasks like the three-word recall test, and is crucial before considering other steps like conferencing with a psychiatrist about medication, scheduling family therapy, or referring the client for cognitive testing.