A measurement of the amount of immunoglobulin molecule with an amino acid sequence that binds to double-stranded deoxyribonucleic acid (DNA), a molecule composed of two anti-parallel, hydrogen-bonded, polymeric strands of nucleic acids in which the sugar is deoxyribose and which is also composed of phosphate groups and any combination of the bases adenine, guanine, cytosine, and/or thymine, in a specified sample of serum, expressed as the last dilution of plasma at which a positive result could be obtained.