Clinical significance
Urea is the cheif nitrogenous waste of mammals. Humans also excrete a second nitrogeneous waste, uric acid. It is the product of nucleic acid, not protein, metabolism. It is produced within perxisomes. Uric acid is the end product of purine metabolism (purines are building blocks of of RNA and DNA). Most uric acid produced in the body is excreted by the kidneys. An overproduction of uric acid occurs when there is excessive breakdown of cells, which contain purines, or the inability of the kidneys to excrete uric acid.
Uric acid is only slightly soluble in water and may precipitate out of solution contributing to the formation of kidney stones. Uric acid may also form needle like crystals in one or more joints producing the excruciating pain of gout. Curiously, our kidneys reclaim most of the uric acid filtered at the glomeruli. Uric acid is a potent antioxidant and thus can protect cells from DNA damage. Humans and apes are susceptable to gout. All other mammals have an enzyme for breaking uric acid down into a soluble product. These animals convert the waste product of protein metabolism -as well as nucleic acid metabolism - into uric acid. Because of its low solubility in water, these animals are able to eliminate waste nitrogen with little loss of water.
Elevated levels:
- Hyperuricemia
- Gout
- Acidosis
- Alcoholism
- Diabetes
- Hypo parathyroidism
- Lead poisoning
- Leukemia
- Neprolithiasis
- Polycythemia vera
- Renal failure
- Toxemia of pregnancy
- Purine-rich diet
- Severe exercise
Decreased levels:
- Fanconi's syndrome
- Wilson's disease
- SIADH
- Low purine diet
Additional conditions under which the test may be performed.
- Chronic gouty arthritis
- Injury of the kidney and ureter