Gout is an inflammatory arthritis of metabolic origin that is caused by crystallization of MSU within joints. It is the most common inflammatory joint disease in men and older women. Its incidence and prevalence are increasing markedly worldwide. The metabolic derangement responsible for gout is the supersaturation of blood and body fluids with the urate ion to the point that crystal formation is possible. At physiologic pH and at normal body temperature, urate is considered to be supersaturated at concentrations of 6.8 mg/dL or greater. Therefore, from a biologic perspective, hyperuricemia is defined as any serum urate level greater than 6.8 mg/dL in both men and women. Although hyperuricemia is a prerequisite for developing gout, only a small percentage (15 to 25%) of all hyperuricemic subjects ultimately develop gout.