A nurse working in the acute care setting has just received laboratory data results. Which of the following clients should the nurse assess first?

A. Platelet count of 148,000/mm³ is slightly below normal but not immediately life-threatening. B. Magnesium level of 2.9 mEq/L is elevated but usually not critical unless very high or symptomatic. C. Potassium level of 5.9 mEq/L is critically high and can cause life-threatening cardiac arrhythmias, especially in a client with recent chest pain—this client requires immediate assessment. D. WBC count of 14,000/mm³ indicates infection but is not as immediately urgent as the hyperkalemia in option C.