A nurse on a medical unit is reviewing the laboratory reports for a client. Which of the following laboratory values is the priority to report to the provider?

A. A creatinine level of 0.4 mg/dL is slightly below the normal range (typically 0.6–1.3 mg/dL) but is not immediately life-threatening. B. A BUN of 9.5 mg/dL is within the normal range (7–20 mg/dL) and not concerning. C. A sodium level of 135 mEq/L is at the lower end of the normal range (135–145 mEq/L), so it's not a priority. D. A potassium level of 3 mEq/L is below the normal range (3.5–5.0 mEq/L) and is priority because hypokalemia can lead to life-threatening cardiac arrhythmias and muscle weakness.