What immediate action should be taken if a client's blood pressure remains elevated after a second measurement?

When a client's blood pressure remains elevated after a second measurement, the most appropriate immediate action is to refer them to a health professional. Elevated blood pressure can be indicative of underlying health issues, and it’s crucial to ensure that the client receives appropriate medical evaluation and management.

An immediate referral is necessary because elevated blood pressure readings can pose a risk to the client's health and may require intervention from a medical professional. In a fitness context, it's important to prioritize the health and safety of clients, and this step ensures that they are assessed by someone qualified to manage potential health concerns.

Other actions, like continuing the session as normal or encouraging increased hydration, do not adequately address the potential risks associated with elevated blood pressure. Reassessing in 10 minutes may not provide timely intervention and could lead to a delay in necessary medical care. Thus, referring the client to a health professional is a proactive and responsible measure to take in this situation.