Uric acid - common data for the parameter, principles of the analytical methods, source of errors and interference, indications for investigation, patient preparation, specimen, reference ranges, result’s interpretation.
Uric acid final product of purine bases breakdown in the organism and from the foods. Purines are found in some foods and drinks, such as liver, anchovies, mackerel, dried beans and peas, beer, and wine. Xanthine and hypoxanthine are intermediate products of this process. Xanthine is oxidized by xanthine-oxidase to uric acid
Uric acid is filtered by the glomerulus, it is reabsorbed in the proximal tubules and is secreted by the distal tubules in the urine. Some of the uric acid present in the gastrointestinal tract is destroyed by bacterial enzymes (uricase) forming allantoin. But if too much uric acid is being produced or if the kidneys are not able to remove it from the blood normally, the level of uric acid in the blood increases. At plasma levels above 430 μmol/l plasmas it saturates and urate crystals may form and precipitate in the tissues.
Principles of the analytical methods: colorimetric; enzymatic (uricase)
Preparation of patient: Blood is obtained under standard conditions. Should not take purine-rich food the day before investigation.
Specimen: serum without hemolysis, urine
Sources of errors: Triglycerides, keto-acids and lactate compete with uric acid for excretion in the renal tubules leading to positive false readings. Uric acid blood levels vary from day to day. The level is usually higher in the morning and lower in the evening. Drugs that can increase the level of uric acid in your body include: Alcohol; Ascorbic acid; Aspirin; Drugs that can decrease the level of uric acid in your body include: Allopurinol, Azathioprine, Oestrogen
Reference range: Male - 208-387 μmol/l Female - 149-363 μmol/l
Interpretation of results:
Elevated levels of uric acid Hyperuricemia: due to purine-rich diet, primary gout, treatment with cytotoxic drugs, hemolytic and megaloblastic anemia, renal diseases
Decreased levels of uric acid: - Hyperuricemia associated with some kinds of liver or kidney diseases (decreased reabsorption in the tubules), exposure to toxic compounds, over dosage of drugs which increase the excretion of uric acid, and rarely as the result of an inherited metabolic defect (xanthine oxidase inhibition)