Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1272 page)

   Colchicine administration

   Limitations

   Methodologic interference (e.g., ascorbic acid, levodopa, methyldopa).

   A purine-rich diet (liver, kidney, sweetbread) as well as severe exercise, increases uric acid values.

   Rapid degradation of uric acid occurs at room temperature in the plasma of patients with tumor lysis syndrome who are treated with rasburicase. Blood should be collected in prechilled tubes containing heparin, immediately immersed in ice water bath, centrifuged in a precooled centrifuge, and the separated plasma maintained in an ice water bath, and it should be analyzed within 4 hours of collection.

URIC ACID, URINE

   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