A nurse is caring for an older adult client who has a new prescription for spironolactone. Which of the following laboratory values should the nurse monitor for this client?

A. Hemoglobin levels are not directly affected by spironolactone; routine monitoring is not required unless there is another underlying condition. B. Total cholesterol is not influenced by spironolactone therapy, so it does not need to be routinely monitored in this context. C. Potassium levels must be closely monitored because spironolactone is a potassium-sparing diuretic. It inhibits aldosterone, which can lead to hyperkalemia, a potentially life-threatening electrolyte imbalance, especially in older adults or those with renal impairment. D. Thyroid stimulating hormone (TSH) is not affected by spironolactone and does not require routine monitoring related to this medication.