An Anti-Histone Antibody (IS/Histo Test) detects autoantibodies against histones (proteins DNA wraps around) in your blood, primarily used to diagnose Drug-Induced Lupus (DIL), a condition caused by certain medications like hydralazine or procainamide, though also found in SLE and other autoimmune issues. This test helps differentiate DIL from other lupus types and monitor disease, often ordered with positive ANA tests when lupus symptoms arise, helping doctors pinpoint if a drug, not primary autoimmunity, is the cause