Gout is a form of inflammatory arthritis characterized by recurrent attacks of a red, tender, hot, and swollen joint. Pain typically comes on rapidly in less than twelve hours. The joint at the base of the big toe is affected in about half of cases. It may also result in tophi, kidney stones, or urate nephropathy. Gout is due to elevated levels of uric acid in the blood. This occurs due to a combination of diet and genetic factors. At high levels, uric acid crystallizes and the crystals deposit in joints, tendons and surrounding tissues, resulting in an attack of gout. Gout occurs more commonly in those who eat a lot of meat, drink a lot of beer, or are overweight. Diagnosis of gout may be confirmed by seeing the crystals in joint fluid or tophus. Blood uric acid levels may be normal during an attack.