Detection of autoantibodies reactive with pancreatic islet cell antigenic molecules and/or insulin

A method of screening an undiluted sample of serum or plasma obtained from an animal subject for analyte autoantibodies reactive with one or more antigenic molecules selected from glutamic acid decarboxylase 65 (GAD65) or glutamic acid decarboxylase 67 (GAD67), said method comprising:

• (a) immobilizing one or more first sources of antigenic molecules to a solid support in an amount so as to form a monovalent intermediate complex comprising [antigenic molecule of said first source]-[analyte autoantibody] capable of forming a divalent complex with antigenic molecules of one or more second sources, wherein said one of more first sources of antigenic molecules is capable of interacting with analyte autoantibodies in a sample of serum or plasma from said subject, or a calibrator and is selected from the group consisting of GAD65, GAD67, and fusion molecules comprising two or more directly or indirectly fused antigenic molecules selected from GAD65 or GAD67;
• (b) contacting said immobilized one or more first sources of antigenic molecules with:
• (1) an undiluted sample of serum or plasma from said subject, or said calibrator;
• and
• (2) one or more second sources of antigenic molecules comprising a direct or indirect label, wherein said one of more second sources of antigenic molecules is capable of interacting with analyte autoantibodies in a sample of serum or plasma from said subject, or said calibrator and is selected from the group consisting of GAD65, GAD67, and fusion molecules comprising two or more directly or indirectly fused antigenic molecules selected from GAD65 or GAD67,
• whereby analyte autoantibodies when present in said sample of serum or plasma interact with said first and second sources of antigenic molecules to form one or more divalent complexes comprising [antigenic molecule of said first source]-[analyte autoantibody]-[antigenic molecule of said second source];
• and
• (c) detecting the presence of complexes formed in (b) to provide an indication of analyte autoantibodies present in said sample.