Laboratory studies Uric acid in 24-hour urine sample d in 24 hours on a regular diet, these patient ci If patients excrete more than of uric a (approximately 10%o of patients with gout) requi re allopurinol instead of probenecid to reduce ur ic acid levels In patients in whom probenecid is contraindicate ed(eg, those with a history of enal insufficiency 15 浙医二院15 浙医二院 Laboratory Studies Uric acid in 24-hour urine sample If patients excrete more than 800 mg of uric aci d in 24 hours on a regular diet, these patients (approximately 10% of patients with gout) requi re allopurinol instead of probenecid to reduce ur ic acid levels. In patients in whom probenecid is contraindicat ed (eg, those with a history of renal stones or r enal insufficiency)