Anti-histone antibodies are autoantibodies that are found in 50%-70% of patients with systemic lupus erythematosus (SLE) and in more than 95% of patients with drug-induced lupus erythematosus.
An ELISA for detecting anti-histone antibodies is said to be positive when there is more than 25 units/ml anti-histone antibodies in a blood sample.
References
Anti-histone antibodies Wikipedia(Text) CC BY-SA