Abstract: A diagnostic element for detecting the presence of anti-dsDNA antibodies in a sample. The diagnostic element includes a support (e.g., a microcell), a coating of mBSA on the support, dsDNA antigens immobilized on the coating, and a blocking layer for blocking immobilization sites other than ones occupied by dsDNA antigens. A testing kit is also provided which includes a diagnostic element, a sample diluent, an antibody solution, and a label identifying solution.