What is the highest priority action when a client has a serum potassium level of 3.3 mg/dL?

When a client has a serum potassium level of 3.3 mg/dL, which is considered low (hypokalemia), the highest priority action is to implement telemetry monitoring. This is crucial because potassium is vital for normal cardiac function, and low levels can lead to serious complications such as arrhythmias, which may be life-threatening. Continuous telemetry monitoring allows healthcare providers to observe any changes in the client’s heart rhythm that could indicate these complications, enabling prompt intervention if necessary.

In this situation, while educating the client on potassium-rich foods and obtaining potassium replacement might be part of the overall treatment plan, they are not immediate actions. Neurological status assessment is also important, but it does not address the direct risk to the client’s cardiac health from the low potassium levels. Therefore, initiating telemetry monitoring is the most appropriate and urgent step to ensure the client's safety.