Claim: A subclass of anti-nuclear antibodies are anti-Sm antibodies.

Antinuclear antibodies -LRB- ANAs , also known as antinuclear factor or ANF -RRB- are autoantibodies that bind to contents of the cell nucleus . In normal individuals , the immune system produces antibodies to foreign proteins -LRB- antigens -RRB- but not to human proteins -LRB- autoantigens -RRB- . In some individuals , antibodies to human antigens are produced .   There are many subtypes of ANAs such as anti-Ro antibodies , anti-La antibodies , anti-Sm antibodies , anti-nRNP antibodies , anti-Scl-70 antibodies , anti-dsDNA antibodies , anti-histone antibodies , antibodies to nuclear pore complexes , anti-centromere antibodies and anti-sp100 antibodies . Each of these antibody subtypes binds to different proteins or protein complexes within the nucleus . They are found in many disorders including autoimmunity , cancer and infection , with different prevalences of antibodies depending on the condition . This allows the use of ANAs in the diagnosis of some autoimmune disorders , including systemic lupus erythematosus , Sjögren 's syndrome , scleroderma , mixed connective tissue disease , polymyositis , dermatomyositis , autoimmune hepatitis and drug induced lupus .   The ANA test detects the autoantibodies present in an individual 's blood serum . The common tests used for detecting and quantifying ANAs are indirect immunofluorescence and enzyme-linked immunosorbent assay -LRB- ELISA -RRB- . In immunofluorescence , the level of autoantibodies is reported as a titre . This is the highest dilution of the serum at which autoantibodies are still detectable . Positive autoantibody titres at a dilution equal to or greater than 1:160 are usually considered as clinically significant . Positive titres of less than 1:160 are present in up to 20 % of the healthy population , especially the elderly . Although positive titres of 1:160 or higher are strongly associated with autoimmune disorders , they are also found in 5 % of healthy individuals . Autoantibody screening is useful in the diagnosis of autoimmune disorders and monitoring levels helps to predict the progression of disease . A positive ANA test is seldom useful if other clinical or laboratory data supporting a diagnosis are not present .