A nurse is evaluating the effectiveness of allopurinol therapy for a client who has chronic gout. Which laboratory finding indicates the medication is achieving the desired therapeutic effect?

A. A white blood cell count of 11,000/mm³ is at the upper limit of normal. While this value is within the reference range, it does not indicate the effectiveness of allopurinol therapy. White blood cell counts are not used to monitor uric acid control or gout management. B. A serum creatinine level of 1.4 mg/dL is elevated above the normal reference range, suggesting possible impaired renal function. Although monitoring renal function is important because allopurinol is excreted by the kidneys, creatinine levels do not reflect whether the medication is successfully lowering uric acid or preventing gout flares. C. A serum uric acid level of 5.8 mg/dL falls within the target reference range of 3.5–7.2 mg/dL. Allopurinol’s primary goal is to reduce uric acid levels to prevent crystal formation and acute gout attacks. A uric acid level within the normal range indicates the medication is achieving its desired therapeutic effect. D. A blood glucose level of 130 mg/dL is elevated above the normal fasting range and may indicate impaired glucose metabolism, but it is unrelated to allopurinol effectiveness. Blood glucose monitoring is not part of assessing gout therapy.