Uric acid in the blood is an indicator of the body’s protein metabolism, reflecting the level of metabolism of purine bases that are part of purine nucleotides. Uric acid test has an independent value, but is more often carried out in conjunction with the determination of urea, creatinine, uric acid (urates) in the urine. Determination of uric acid concentration is used in the diagnosis of uric acid diathesis, determining the risk of cardiovascular complications, renal dysfunction, and evaluating the effectiveness of treatment. Plasma isolated from venous blood is used for uric acid test. As a rule, the determination of this indicator is carried out by the phosphor-tungsten method. The range of fluctuations in the level of uric acid in a healthy adult is from 150 to 420 mmol/l. The readiness of the analysis results is one working day.
Uric acid is the final product of purine metabolism. Purines are required by the body for the synthesis of DNA and RNA. As a result of enzymatic cleavage of nucleotides, purine bases are formed – guanine and adenine, which in turn are deaminated to hypoxanthine and xanthine. The latter under the action of the enzyme xanthine oxidase is converted into uric acid. The concentration of uric acid depends on the equilibrium of its synthesis and excretion processes. 70-80% of the metabolite is excreted by the kidneys in the urine, 20-30% through the intestine with feces and about 1% in saliva.
According to WHO, an increased concentration of uric acid in the blood – hyperuricemia – is present in 2% of the world’s population. The male half of humanity under the age of 65 suffers from hyperuricemia 15 times more often than the female. Excessive levels of urates in the blood accompany and aggravate the course of heart disease and diabetes mellitus. However, studies have shown that uric acid has some useful properties. Its antioxidant activity protects the body from the effects of harmful free radicals. With a slight increase in the level of this metabolite in the blood, intellectual abilities improve.
Uric acid test is most often used to establish the diagnosis of gout and evaluate the effectiveness of treatment with anti-gouty agents in rheumatology. In nephrology and urology, the study is performed as part of a comprehensive biochemical analysis to assess the severity of chronic kidney disease; in cardiology – to determine the risk factor of an unfavorable prognosis of cardiovascular diseases; in neurology – to determine the cause of neuroses.
Indications and contraindications
Uric acid test is prescribed in combination with a study of rheumatoid factor and C-reactive protein for prolonged persistent pain syndrome in the joints and ligaments, especially with severe pain in the area of the big toes. These symptoms may indicate the deposition of sodium salts of uric acid in the body. A sign of long-term hyperuricemia is the formation of nodules above the joints (tofuses). If the patient’s direct relatives suffer from gout, uric acid examination will help to identify early asymptomatic hyperuricemia. Timely lifestyle changes and treatment will help to avoid serious complications.
Uric acid test together with the determination of urea and creatinine is carried out with a decrease in the amount of urine excreted, the occurrence of edema in the lower legs, lower back, face, an increase in the circumference of the abdomen. These symptoms may indicate fluid retention due to a drop in filtration function of the kidneys. Determination of the indicator in blood and urine is carried out with pain in the lumbar region, the appearance of blood in the urine, frequent and painful urination, fever. Such symptoms may indicate the deposition of urates in the kidneys and the development of urolithiasis.
The analysis is indicated for dizziness, headache, nausea, distraction, sleep disorders, irritability and sudden attacks of aggression. These symptoms may indicate the toxic effect of an overabundance of the metabolite on brain tissue and the development of uric acid diathesis. The level of uric acid concentration in the blood determines the risk of atherosclerosis, hypertension; the likelihood of vascular catastrophes – stroke and myocardial infarction. The analysis is performed to monitor the effectiveness of the treatment of metabolic syndrome, renal insufficiency, radiation and chemotherapy for oncological diseases.
Therapeutic and diagnostic interventions on the pelvic organs (X-ray, trans-rectal ultrasound and trans-vaginal ultrasound, proctological manipulations, physiotherapy, etc.) should be spaced in time with blood sampling for uric acid, because they can distort the true results of laboratory research.
Preparation and blood collection
To uric acid test, blood taken in the morning (before 11:00) is used. Blood is taken in the laboratory, the treatment room of a polyclinic or inpatient department from the ulnar vein or venous catheter. At home, a portable analyzer with special test strips can be used to self-monitor the level of the metabolite. In this case, capillary blood is used.
For the greatest reliability of the results, it is necessary to follow some recommendations. Within 3-5 days, you need to adhere to a low-purine diet, refrain from taking alcohol or be sure to warn your doctor about it. Athletes should exclude the use of dietary supplements with proteins and testosterone production stimulants. During the day before taking the analysis, you can not expose yourself to intense physical exertion. 8-12 hours before taking blood, it is necessary to stop eating, drink only clean water. 30 minutes before the study, you should not smoke and expose yourself to psychoemotional overstrain.
Several milliliters of blood are collected in a dry, clean test tube or a vacuum tube with a lid. The identification number of the analysis, the time and place of blood sampling are indicated on the test tube. The blood can be stored at room temperature for an hour before the test tube is handed over to a courier or a laboratory assistant. If transportation is delayed, then the test tube is placed in a refrigerator or a special container. The blood is delivered to the biochemical laboratory on the same day.
To determine uric acid, colorimetric and enzymatic methods are most often used. The unified method is the colorimetric phosphor-tungsten method. In the laboratory, a reagent, sodium tungsten acid, is added to the blood serum, mixed and filtered. The solution is colored blue. Further, the concentration of the compound is determined by the photokinetic method based on the intensity of staining of the solution.
Depending on the urgency and equipment of the laboratory, the study is carried out from a few minutes to several hours after blood sampling. As a rule, the tests are given to the doctor or patient in the evening of the same day or the next day.
Normal values
In children under 1 month, the uric acid level is in the range of 80-311 mmol/l, from 1 month to 1 year – 90-372, from 1 year to 14 years – 120-362 mmol /l. In adult women, the concentration in the blood is 150-350 mmol / l, in men – 210-420 mmol / l. According to some studies, due to aging and cell death, a decrease in the filtration function of the kidneys, the norm of the indicator in the population over 60 years of age is 500 mmol/ l. In people with blood group III (B), the level is slightly higher.
A slight (physiological) change in the level of uric acid in the blood may be associated with physical exertion due to increased testosterone synthesis. The latter has a pronounced anabolic effect, retains phosphorus and nitrogen in the body, thereby stimulating the formation of nucleotides. Eating a large number of foods with a high purine content (red meat, liver, protein shakes, fish, legumes, coffee, chocolate, alcohol) increases the level of the metabolite in the blood.
Physiological short-term hyperuricemia occurs when smoking due to a temporary lack of oxygen supply to the tissues of the body. The concentration of the compound increases with excessive solar insolation. At the same time, uric acid acts as a natural antioxidant and is produced in order to protect the body from the harmful effects of free radicals formed under the influence of ultraviolet rays. In the first and second trimester of pregnancy, the level of uric acid is slightly reduced, in the third trimester it is physiologically increased.
Increased blood levels
The most common diseases in which there is an increased level of uric acid are gout and uric acid diathesis. The reasons for the increase in these cases are the consumption of food with a high purine content, accelerated synthesis of purine nucleotides, inhibition of excretion of the metabolite in the urine and hereditary predisposition. The excretion of uric acid from the body worsens with diseases of the kidneys and urinary tract. Diseases such as pyelonephritis, polycystic kidney disease, urolithiasis (kidney stones), lead to a decrease in the filtration function of the glomeruli and an increase in the level of the indicator in the blood.
Oncological diseases, including leukemia, radiation and chemotherapeutic effects on tumors increase the concentration of this compound. The increase in the level of the degradation product of nucleic acids is associated with the mass death of cells and the need for accelerated construction of new tissues to replace the “dead”.
An increased indicator is found in insulin-resistant conditions: diabetes mellitus, metabolic syndrome, obesity. The cause of hyperuricemia is an overabundance of insulin in the body, the effect of which reduces the reabsorption of uric acid in the renal tubules. Aspirin, diuretics, some antitumor drugs, metoprolol, corticosteroids contribute to an increase in the concentration of urates in the blood.
Excessive uric acid content is one of the symptoms of congenital hereditary pathologies: Lisch-Nihan and Kelly-Sigmiller syndromes, Down’s disease. In these cases, there is a genetic “breakdown” at the level of the enzymatic systems involved in the formation of the compound. The excretion of uric acid is disrupted in other diseases of organs and tissues. The cause may be hypertension, heart failure, lead poisoning, hemolytic anemia.
Decrease in blood levels
A decrease in the level of uric acid in the blood is likely in liver diseases: hepatitis, including alcoholic, cirrhosis of the liver, fatty hepatosis. The reasons for the decrease are the inhibition of the production of enzymes involved in purine metabolism. A transient decrease in uric acid levels may occur during pregnancy in the first two trimesters due to an increase in blood volume and accelerated filtration in the kidneys. Allopurinol, azathioprine, fibrates, contrast agents reduce the level of urates.
The reason for the decrease in the amount of the compound in the blood is the Wilson-Konovalov syndrome. Violation of copper metabolism leads to cirrhosis of the liver. Liver cell damage reduces the activity of xanthinoksidase. Fanconi syndrome reduces the indicator due to a defect in the development of kidney tubules. The reverse absorption of the metabolite decreases, the excretion of urates in the urine increases.
Treatment of abnormalities
Elevated levels of uric acid do not indicate one hundred percent development of gout. With the result of a biochemical analysis, you should consult a doctor to determine the cause of hyperuricemia and decide on the use of special drugs. Nutrition adjustment is one of the most effective methods of restoring the balance of uric acid in the body. The number of high-protein products is excluded or sharply limited: red meat, liver, kidneys, fish, smoked meats, marinades, tomatoes, eggplants, coffee drinks, chocolate, alcohol. The introduction of vegetables and fruits, fresh juices, dried fruits, honey, poultry meat into the diet contributes to the reduction of uric acid.
With a small increase in urates in the body, recipes of traditional medicine help. A decoction of birch or lingonberry leaves perfectly copes with the removal of “excess” uric acid from the body. It is recommended to take 2-3 liters of clean drinking water daily. Regular physical activity activates metabolic processes and promotes the excretion of uric acid. Athletes, on the contrary, are shown to reduce power loads.
