Final answer:
The first step when admitting a client with decreased circulation in the left leg is to assess vital signs for an immediate understanding of the patient's health status.
Step-by-step explanation:
The initial action the nurse should take when admitting a client with decreased circulation in the left leg is a) Assess vital signs. This step is crucial as it helps establish a baseline for the patient's overall health status and identifies any immediate concerns that may require urgent attention. After assessing vital signs, the nurse may elevate the leg or apply warmth, but only after discussing the case with a physician. Notifying the physician is also important for proper management, but it does not replace the immediate need to assess the patient's condition.