A patient on furosemide reports muscle weakness and dizziness. Which laboratory value should the nurse check?

Choice A rationale Serum sodium levels are important to monitor, as furosemide can cause hyponatremia (normal range 135-145 mEq/L). However, muscle weakness and dizziness are more classic signs of hypokalemia, as potassium plays a crucial role in nerve and muscle function. Therefore, potassium is the more critical value to check initially. Choice B rationale Furosemide is a loop diuretic that inhibits the reabsorption of sodium and chloride in the loop of Henle, leading to increased excretion of water, sodium, potassium, and chloride. The patient's symptoms of muscle weakness and dizziness are classic manifestations of hypokalemia (normal range 3.5-5.0 mEq/L), making serum potassium the most important lab value to check. Choice C rationale While loop diuretics can sometimes affect blood glucose levels, leading to hyperglycemia, this is not a primary concern for the immediate symptoms of muscle weakness and dizziness. These symptoms are much more indicative of an electrolyte imbalance, specifically potassium, which is directly affected by furosemide's mechanism of action. Choice D rationale Serum calcium levels can also be affected by furosemide, which can cause hypocalcemia. While hypocalcemia can present with muscle cramps and weakness, hypokalemia is a more common and prominent side effect of loop diuretics. Thus, checking potassium levels is the priority given the reported symptoms.