Hypouricemia is arbitrarily defined as a serum urate concentration of less than 2 mg/dL (119 micromol/L). It occurs in about 2 percent of hospitalized patients and less than 0.5 percent of the normal population . Hypouricemia may be caused by decreased uric acid production, uric acid oxidation due to treatment with uricase, or decreased renal tubular reabsorption due to inherited or acquired disorders . There are no known abnormalities of intestinal uricolysis that produce hypouricemia. (See "Uric acid balance".)
Hypouricemia has been thought of as a biochemical disorder with no clinical significance other than as a marker of underlying disease . However, individuals with renal tubular urate wasting may have an increased incidence of acute kidney injury (previously called acute renal failure). (See "Definition of acute kidney injury (acute renal failure)".)
Decreased uric acid production can be caused by several rare inherited disorders of purine synthesis and catabolism and, more commonly, by acquired deficiency of xanthine oxidase due to allopurinol therapy or liver disease.
Inherited disorders — Inherited disorders resulting in decreased uric acid production include hereditary xanthinuria and purine nucleosidase phosphorylase deficiency:
●Hereditary xanthinuria − Xanthine oxidase catalyzes the conversion of hypoxanthine to xanthine and of xanthine to uric acid. Deficiency of xanthine oxidase, which is inherited as an autosomal recessive trait, results in hereditary xanthinuria [4,5]. Striking hypouricemia is seen with levels usually below 1 mg/dL (59.5 micromol/L). Increased urinary excretion of relatively insoluble xanthine leads to the development of xanthine stones in approximately one-third of patients. Xanthine stones are managed with fluids to increase the urine output (which reduces the urine xanthine concentration) and with alkali administration (which modestly increases xanthine solubility) . In a smaller number of patients, deposition of xanthine crystals in skeletal muscle produces myopathic symptoms.
The diagnosis is suspected by the finding of hypouricemia, reduced urinary uric acid excretion, and increased xanthine excretion; it is confirmed by liver or intestinal biopsy with measurement of enzyme activity.