Hyperuricosuria, renal handling

EVIDENCE OF ABNORMAL RENAL HANDLING OF URIC ACID IN PATIENTS WITH NEPHROLITHIASIS AND HYPERURICOSURIA... 

A group of patients forming calcium oxalate stones are hyperuri-cosuric and it is thought that their excessive urate excretion contributes to calcium-stones formationl. The pathomechanisms invoked are dietary purine excess and endogenous uric acid overproduction, being defective tubular reabsorption of urate "unattractive because uricemia was found to be normal in patients with recurrent calcium nephrolithiasis (RCN) and hyperuricosuria. Current studies were undertaken to define the incidence, role of diet, abnormalities of the renal handling of urate, and associated metabolic disturban-c"es in patients with RCN and hyperuricosuria. 

Fifty patients (22 males and 28 females mean age 46 years) were consecutively referred to our Metabolic Unit for the evaluation of recurrent nephrolithiasis. Diagnosis was made on the basis of spontaneous emission or chirurgical extraction of two or more calculi with an interval superior to one year. In every patient we performed a metabolic study and the results were compared with those obtained in 20 controls (10 males and 10 females mean age 33 years) Hyperuricosuria was defined as daily uric acid excretion above 800 mg for men and 750 mg for woman, while on a purine-free diet. Renal handling of uric acid ms evaluated by means of pyrazinamide (PZA) and probenecid (PB) tests. ... 

Data concerning renal handling of uric acid appears in Table 2. The administration of an essentially purine-free diet normalized uricosuria in 4 patients. PZA and PB tests were within normal limits in these patients, suggesting that hyperuricosuria could be related to purine overingestion. Five patients remained hyperuricosuric even under an essentially purine-free diet, and 2 were hypo-... 

Dietary habits and tubular transport defects of urate explain the excessive uric acid excretion of patients with RCN. An alteration of the renal handling of uric acid may be suspected when hyperuricosuria concurs with hypouricemia normal serum uric acid does not exclude a tubular transport defect of urate. 

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