ANA, or antinuclear antibody, is an antibody in the blood that may indicate the propensity of an individual to mount an autoimmune response, which is an attack against a part of one's own body. ANA specifically targets the nucleus of a cell. While elevated ANA is common and does not necessarily indicate a disease, the more elevated the level, the more concerning for an underlying problem. We measure the level based upon the titer, which tells us how much the blood has to be diluted before the ANA can no longer be detected; titers above 1:40 are considered positive (although still low and often of no real significance). A titer of 1:647 is very high and warrants additional testing for an autoimmune disease. The classic disease associated with this is systemic lupus erythematosis (SLE, or lupus), although other diseases may involve an elevated ANA as well, such as scleroderma, Sjogren's syndrome, primary biliary cirrhosis, autoimmune hepatitis, and Raynaud's syndrome. Your symptoms sound quite suggestive of SLE. This disease can affect multiple systems throughout the body. Diagnosing it is difficult because there is no single "lupus" test and the symptoms widely vary from person to person. Fulfillment of four out of 11 possible criteria (symptoms and blood tests) strongly suggests the diagnosis. Your doctor can examine you and determine the appropriate testing to further assess for the possibility of lupus or another autoimmune disorder.