Uric Acid in Urine

Introduction

Human urine contains water and other compounds like urea, uric acid, sodium, potassium, chloride, sulfate, ammonium, phosphate, and a few ions and molecules. Uric acid is the normal component of urine, constituting 0.03 %. It is also present in blood and in trace amounts in various organs of the body. Variations in the levels of uric acid are seen in certain pathological conditions.

What Is the Significance of Uric Acid?

Uric acid has a significant physiological role in the human body. Uric acid is filtered in the glomeruli of the kidneys, and 90 % of uric acid that is filtered in the kidney is reabsorbed. Uric acid takes part in the following functions.

• Antioxidant - Uric acid is a potent antioxidant, peroxynitrite scavenger, and a strong reactive oxygen species. High levels of uric acid are identified in the cytosol of the cells like liver cells, vascular endothelial cells, and nasal secretions, where the uric acid serves the function of antioxidant.

• Endothelial Function - Low levels of serum uric acid cause endothelial dysfunction. Though uric acid impairs endothelial integrity and causes cardiovascular and kidney diseases, it may help in tissue healing by initiating the inflammatory process that is essential for tissue repair, mobilizing progenitor endothelial cells, and scavenging oxygen free radicals.

• Immune Responses - Uric acid is a mediator of type II immune responses. Uric acid initiates protective antibody responses to various vaccines incorporating alum as an adjuvant. It initiates and amplifies allergic inflammation. It mediates type II immune responses involving epithelial cells, eosinophils, innate lymphoid cells, basophils, and mast cells.

• Resistance to Parasites - Uric acid has the potential to protect against infectious diseases like schistosomiasis caused by Schistosoma. Uric acid plays a role in stimulating fatty acid synthesis and releasing unsaturated fatty acids like arachidonic acid. It also interferes with lipoxygenase activity and acts as a substrate for the cyclooxygenase enzyme. Hence, arachidonic acid accesses the parasites and diminishes them.

• Defense Mechanism - Uric acid plays a defensive role against neurological and autoimmune diseases. Low levels of uric acid decrease the antioxidant molecules. Peroxynitrites and reactive oxygen species are responsible for myelin degradation, which can be corrected with high levels of uric acid. Low plasma uric acid is seen in neurological disorders, Parkinson's and Alzheimer’s disease, pemphigus vulgaris, and lichen planus.

Despite its physiological functions, uric acid also has pathogenic potential. Variations in uric acid levels can cause various disorders. Uric acid is the main etiological agent of acute and chronic inflammatory arthritis and gout. It is also responsible for the initiation and progression of metabolic syndrome.

What Is Uric Acid in Urine?

Urine is the liquid waste that is produced in the kidneys. It contains water and various organic and inorganic compounds. Uric acid is an organic compound that is made of carbon, nitrogen, oxygen, and hydrogen. Uric acid is produced in the liver, intestines, and other tissues like muscles, kidneys, and the vascular endothelium during purine metabolism. It is also produced when the live and dying cells' nucleic acids, adenine, and guanine, undergo degradation. Uric acid is eliminated through the kidneys. Low uric acid concentrations in urine are known as hypouricosuria, and high concentrations of uric acid in urine are known as hyperuricosuria. Hyperuricosuria and hypouricosuria are associated with pathological conditions.

What Is Hyperuricosuria?

Hyperuricosuria indicates excessive daily urinary uric acid excretion levels of more than 750 mg in women and more than 800 mg in women. It can be due to congenital and acquired causes that increase uric acid secretion or diminish the elimination of uric acid. Hyperuricosuria can be an acute or chronic condition.

Acute hyperuricosuria occurs as a complication of tumor lysis syndrome. Chronic hyperuricosuria is a complication of gout and uric acid nephrolithiasis, but it can occur even without hyperuricosuria. Hyperuricosuria is seen in the following medical conditions:

• Gout.

• Acute uric acid nephropathy.

• Acute kidney failure.

• Leukemia.

• Uric acid nephrolithiasis (uric acid kidney stones).

• Tumor lysis syndrome.

• Fanconi syndrome.

• Dent’s disease.

• Lesch-Nyhan syndrome.

• Rhabdomyolysis.

• Myeloproliferative disorders like multiple myeloma.

• Cancer metastasis.

• High-purine diet.

• Obesity.

In the absence of hyperuricemia and gout, the risk of uric acid nephrolithiasis due to hyperuricosuria is managed with antiuricosuric drugs.

What Is Hypouricosuria?

Hypouricosuria indicates the excretion of low levels of uric acid in urine. Low uric acid in urine can be due to the following conditions:

• Impaired ability to excrete uric acid as a result of chronic kidney diseases.

• Chronic glomerulonephritis.

• Lead poisoning.

• Chronic alcohol use.

What Is Uric Acid Urine Test?

Uric acid is produced during the metabolic breakdown of purines. Purines are substances that are present in the cells and certain foods like liver, anchovies, dried beans, beer, and sardines. The uric acid dissolves in blood and reaches the kidneys, and it is excreted in the urine. A uric acid urine test is performed to determine the uric acid level in urine. It can also be detected using a blood test.

A 24-hour urine sample is collected to measure the uric acid level. This test is performed to determine the cause of high uric acid concentration in the blood. It is performed to monitor individuals with gout and to choose the medications to lower uric acid levels. It is also monitored in individuals under cancer treatments because chemotherapy and radiotherapy increase uric acid levels. It is also done to detect if a high uric acid level in the urine is the reason for kidney stones.

Normal excretion of uric acid in urine is between 500 and 600 milligrams every 24 hours. More than 800 milligrams is excess and considered abnormal. It may be due to a high purine diet or other medical conditions. Excessive uric acid in urine is interpreted as hyperuricosuria, and low uric acid in urine is known as hypouricosuria.

Conclusion

Uric acid is a normal physiological component of urine. Variations in uric acid levels are seen in certain pathological conditions. Urine analysis helps in identifying uric acid levels. The uric acid urine test also monitors uric acid levels in certain conditions. Uric acid is a compound with physiological and pathological functions. Hence, the uric acid urine test is performed to diagnose the prevailing pathological condition.