[Hypouricemia, an old subject and new concepts].

DEFINITION OF HYPOURICEMIA: Hypouricemia (serum uric acid less than 120 micro mol/l) is a biological abnormality often discovered accidentally and with a low prevalence depending on its permanent or transitory nature ranging from 0.15 to 3.38%. NEW PHYSIOLOGICAL CONCEPTS OF ITS PATHOGENESIS: Recently, our knowledge of the physiopathological mechanisms of hypouricemia has been emphasized by the identification of three systems of renal and extra-renal uric acid transport: a Cl/urate (URAT1) transporter, a multispecific organic anion transporter (OAT) and a urate transporter/channel. ETIOLOGY AND COMPLICATIONS OF HYPOURICEMIA: Through questioning, drugs and toxics (allopurinol.) are generally rapidly recognized as responsible for half of the hypouricemia encountered. It can be concomitant to a known disease: severe liver disease, neoplasia, diabetes, AIDS, syndrome of inappropriate antidiuretic hormone secretion. Hypouricemia can also be isolated and justifies the measurement of uric acid clearance, the normality or reduction of which orients towards a deficiency in xanthine-oxydase, the increase in which suggests an abnormality in uric acid transport in the proximal tubule (Fanconi syndrome, primary hereditary anomaly of tubular uric acid transport). Hypouricemia does not appear to expose the patient to any danger, but the onset of nephrolithiasis or acute renal failure secondary to the combination of severe hypouricemia and oxidant stress is always possible.