Uric acid in the urine

Uric acid excreted in urine reflects dietary purine intake and the breakdown of endogenous purine nucleotides. Approximately 70% of the total body uric acid is excreted in urine. Uric acid clearance is 10% of the amount filtered. Renal excretion of uric acid is a function of the amount filtered, which is almost entirely reabsorbed in the proximal tubule, and secretion and reabsorption in the distal tubule.

Determination of uric acid in urine should be carried out together with its determination in blood. In many cases, this allows to establish the pathological mechanism underlying gout in the patient (excessive production of uric acid in the body or impaired excretion). A sign of hyperproduction of uric acid in the body is its excretion in urine of more than 800 mg / day in the case of conducting the study without dietary restrictions or 600 mg / day with a low-purine diet. Before conducting the study, it is necessary to make sure that the kidneys function is normal (in case of decreased creatinine clearance, a decrease in uric acid excretion does not exclude its hyperproduction), and also to exclude possible effects of drugs on the excretion of urates. In case of impaired excretion, a high concentration of uric acid in the blood is not accompanied by an increase in its content in the urine.

Reference values (norm) of uric acid content in urine

	Uric acid content
Type of diet	Mg/day	Mmol/day
Regular diet	250-750	1.48-4.43
Purine-free diet:
Men	Up to 420	Up to 2.48
Women	Up to 400	Up to 2.36
Low Purine Diet:
Men	Up to 480	Up to 2.83
Women	Up to 400	Up to 2.36
High Purine Diet	Up to 1000	Up to 5.90

Determining the mechanism of gout development helps the clinician to choose a treatment regimen for the patient. In case of increased uric acid production, xanthine oxidase inhibitors are prescribed - an enzyme that plays a key role in the formation of uric acid in the body. The dose of the drug (allopurinol) should be selected so that the decrease in uricemia is no more than 35.7-47.6 μmol/l. In case of impaired uric acid excretion, uricosuric agents that block tubular reabsorption of uric acid in the kidneys are prescribed or increased, or these drugs are used in combination with diet therapy. When prescribing uricosuric agents, it should be remembered that increased excretion of uric acid increases the risk of urate stones, which can be reduced by prescribing plenty of fluids.

In the first months (1-4 months) of gout therapy, the main criterion for effectiveness is achieving a serum uric acid concentration in men below 0.36 mmol/l (ideally 0.24-0.30 mmol/l), in women - below 0.3 mmol/l. If the uric acid concentration does not decrease below 0.4 mmol/l, urates do not dissolve in the extracellular fluid and tissues and the risk of gout progression remains.