Uric Acid, Urine

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Subject: Uric Acid, Urine

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Definition

  • Uric acid is produced in the liver from the degradation of dietary and endogenously synthesized purine compounds. The normal male adult has a total body urate pool of approximately 1,200 mg, twice that of the female adult. This gender difference may be explained by an enhancement of renal urate excretion due to the effects of estrogenic compounds in premenopausal women. Under normal steady state conditions, daily turnover of 60% of the urate pool is achieved by balanced production and elimination of uric acid. Human tissues do not have the ability to metabolize urate. Therefore, to maintain homeostasis, urate must be eliminated by the gut and the kidney. The entry of urate into the intestine is most likely a passive process that varies with serum urate concentration. Intestinal tract bacteria are able to degrade uric acid. This breakdown process is responsible for approximately one third of total urate turnover and accounts for nearly all urate disposed of by extrarenal routes. Under normal conditions, uric acid is almost completely degraded by colonic bacteria, with little being found in the stool. Urinary uric acid excretion accounts for the remaining two thirds of the uric acid turned over daily.

  • Normal range:

    • Twenty-four–hour urine: 250–750 mg/day

    • Random urine:

      • Male: 104–593 mg/g creatinine

      • Female: 95–741 mg/g creatinine

Use

  • Diagnosis of kidney stones

  • Monitoring of people with gout, since many of these patients develop uric acid kidney stones

Interpretation

Increased In

  • Gout

  • Renal failure

  • Leukemia

  • Multiple myeloma

  • Lymphoma

  • Toxemia of pregnancy

  • Lesch-Nyhan syndrome

  • Down syndrome

  • Polycystic kidney disease

  • Chronic lead nephropathy

Decreased In

  • Wilson disease

  • Fanconi syndrome

  • Some malignancies

  • Low-purine diet

  • Folic acid deficiency

Limitations

  • Hyperuricosuria is present in patients with renal calculus formation. Even mild renal failure decreases uric acid excretion. Uric acid excretion is decreased with hypertension.

  • Urine uric acid levels are elevated in states of uric acid overproduction such as in leukemia and polycythemia and after intake of food rich in nucleoproteins.

  • High levels of bilirubin and ascorbic acid may interfere with measurement.

  • Rasburicase (Elitek) causes enzymatic degradation of uric acid within blood samples left at room temperature resulting in spuriously low uric acid levels. To ensure accurate measurements in patients who have received rasburicase, blood must be collected into prechilled tubes containing heparin anticoagulant and immediately immersed and maintained in an ice bath; plasma samples must be assayed within 4 hours of sample collection.

 
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