A nurse is reviewing the laboratory report for a client who has been taking sodium polystyrene sulfonate. Which of the following findings indicates a therapeutic response to the medication?

Choice A rationale Magnesium levels within the normal range (1.3 to 2.1 mEq/L) are important for overall electrolyte balance, but sodium polystyrene sulfonate specifically targets potassium. While hyperkalemia can sometimes be associated with other electrolyte imbalances, a normal magnesium level does not directly indicate a therapeutic response to sodium polystyrene sulfonate, as its primary action is not on magnesium. Choice B rationale Calcium levels within the normal range (9 to 10.5 mg/dL) are essential for various physiological functions. Sodium polystyrene sulfonate primarily exchanges sodium ions for potassium ions, not calcium. Therefore, a normal calcium level does not reflect a therapeutic response to the medication, which is specifically aimed at reducing elevated potassium levels. Choice C rationale Sodium levels within the normal range (136 to 145 mEq/L) are crucial for fluid balance and neurological function. Sodium polystyrene sulfonate exchanges sodium for potassium, meaning it increases the body's sodium load. While a normal sodium level is desirable, it does not directly indicate the therapeutic efficacy of the medication in reducing potassium. Choice D rationale Potassium 4.8 mEq/L (3.5 to 5 mEq/L) indicates a therapeutic response. Sodium polystyrene sulfonate is an ion-exchange resin used to treat hyperkalemia by exchanging potassium ions for sodium ions in the gastrointestinal tract. A potassium level returning to within the normal range, from a previously elevated state, signifies that the medication has effectively lowered the excess potassium.