A nurse is assessing a client who is prescribed spironolactone. Which of the following laboratory values should the nurse monitor for this client?

Spironolactone is a potassium-sparing diuretic that blocks aldosterone receptors, causing sodium and water excretion while retaining potassium. This can lead to hyperkalemia (elevated potassium), which can cause life-threatening cardiac arrhythmias. Serum potassium must be monitored closely. Urine ketones, bilirubin, and platelet count are not primary concerns with spironolactone therapy.