hyperuricosuria

Hyperuricosuria is the condition of excessive uric acid excretion in urine. It is defined by urinary uric acid elimination that exceeds the normal upper limit on a 24-hour urine collection, a threshold often cited as around 800 mg per day in adults. Hyperuricosuria can occur with normal or elevated serum uric acid and is a distinct consideration from hyperuricemia. It may contribute to kidney stone formation, particularly uric acid stones.

Causes of hyperuricosuria are grouped as primary or secondary. Primary hyperuricosuria results from inherited abnormalities of renal urate transporters, leading to increased urate excretion. Secondary forms arise with high cell turnover or tissue breakdown (for example, tumor lysis syndrome, hematologic malignancies, extensive psoriasis), renal impairment, dehydration, or medications. Lifestyle factors such as a high-purine diet, excess alcohol intake (notably beer), and excessive fructose can raise uric acid production and excretion. Certain diuretics and other drugs can also influence uric acid handling by the kidneys.

Most people with hyperuricosuria are asymptomatic. When symptoms occur, they are typically related to uric acid nephrolithiasis or crystal-induced renal irritation, presenting as flank pain, hematuria, or recurrent kidney stones. Urine pH is often acidic, and urinalysis may show needle-like uric acid crystals.

Diagnosis relies on a 24-hour urine collection showing elevated uric acid excretion, supported by serum uric acid testing and measurements such as the fractional excretion of uric acid. Imaging may be used to detect stones in patients with suggestive symptoms.

Management focuses on reducing uric acid excretion and preventing stones. Hydration, a diet limiting purines and fructose, weight management, and urine alkalinization (often with potassium citrate) to keep pH around 6.5–7.0 are commonly recommended. Pharmacologic treatment may include urate-lowering therapy (for example, allopurinol or febuxostat) to reduce uric acid production, particularly when hyperuricosuria accompanies hyperuricemia or gout.