Uric Acid: Function & Diseases

Uric acid is the end product of purine metabolism. Purine is necessary for the construction of ribonucleic acid (RNA) as well as deoxyribonucleic acid (DNA), which are found in the body’s cells and carry genetic information.

What is uric acid?

Purine is ingested with food (e.g., meat) and is therefore nonessential. Uric acid is formed during purine metabolism and is excreted in the urine through the kidneys or intestines. Uric acid is only extremely slightly soluble in the blood, with solubility being determined by the pH value. If the urine pH is 7.0, for example, uric acid excretion is ten times worse than at a pH of 5.7. If purine metabolism is disturbed and urine concentration increases, this can lead to various diseases.

Function, effect, and tasks

Uric acid is formed as a degradation product of purine bases, and it is formed from xanthine or hypoxanthine. Seventy-five percent of uric acid is excreted by the kidneys, with the remainder excreted by the intestines, saliva, or sweat. The amount of uric acid in the body depends on gender, age and diet. In men, uric acid levels range between 3.6 mg/dl (lower limit) and 8.2 mg/dl (upper limit), in women between 2.3 mg/dl (lower limit) and 6.1 mg/dl (upper limit). Uric acid levels are determined predominantly in the following diseases:

  • Renal insufficiency
  • Leukemia
  • Radiotherapy or chemotherapy
  • Joint inflammation
  • Diabetes type II
  • Obesity

The concentration of uric acid is measured in both urine and blood serum in the process. Therefore, no alcohol or offal should be ingested for three days before blood sampling. In the blood, uric acid has an antioxidant effect and also protects the blood vessels from damage that can occur due to oxidative processes. If the uric acid level increases very much, crystals are formed from the acid, which can be deposited in the kidneys or joints.

Formation, occurrence, properties and optimal values

Purine bodies are composed of two nitrogen-containing rings. They are found in RNA or DNA but also in energy carriers (e.g., GTP, ATP). In the RNA or DNA molecule, the nitrogen bases adenine and guanine are found, which play an essential role in energy metabolism. During the degradation of the two purine derivatives, the phosphate residue is first cleaved off with the help of certain enzymes, followed by the separation of the base from the sugar. Uric acid is then formed from the nitrogen base via various reactions. The acid is formed in the small intestine and in the liver, whereby a part is formed by the endogenous purine degradation, the other part is formed from purines, which are ingested with food. There are foods that contain a lot of purines and can be of both plant and animal origin. If foods that are rather low in purines are ingested, the body can eliminate the uric acid that is formed during the breakdown process with the urine without any problems. If foods rich in purine are consumed, the metabolism also produces a lot of uric acid, which often cannot be excreted in its entirety. Therefore, it remains in the blood and the uric acid level rises. In addition, there are products that are purine-free, but which nevertheless raise the uric acid level because they inhibit the excretion of uric acid and promote the breakdown of purine. This group mainly includes alcoholic beverages such as beer or schnapps. Another source is fructose, especially when used as a sweetener. If fructose is broken down, the uric acid level rises very sharply and the risk of gout is increased. When there is an increased concentration of uric acid in the blood, physicians speak of so-called hyperuricemia. A distinction is made between primary or secondary hyperuricemia:

Diseases and disorders

When the concentration of uric acid is high, so-called uric acid crystals are formed, especially in the joints. This causes inflammatory reactions and the affected person suffers a gout attack. The excess uric acid is subsequently deposited in the tissue, with the toe and finger joints or the kidney being particularly affected.The uric acid crystals cause severe pain and also lead to functional disorders and deformities. The deposits cause kidney stones or inflammation. In order to reduce elevated uric acid levels, patients should eat a low-fat diet and avoid alcohol. If the uric acid level nevertheless remains elevated, medication must be taken to reduce the production of uric acid. The elevated uric acid levels in gout and also in Lesch-Nyhan syndrome are genetically determined. In addition, a too high uric acid level can have the following reasons:

  • Kidney dysfunction
  • Increased formation of purine in the body
  • Increased intake of purine through the diet

In addition, the body forms increased uric acid at:

Too low uric acid occurs when there is a deficiency of xanthine oxidase or when taking drugs such as probeneciol or allopurinol.