The DIASTAT® anti-Scl-70 test is a qualitative enzyme-linked immunosorbent assay (ELISA) for the detection of autoantibodies specific for Scl-70 antigen in human serum or plasma. It is intended to aid in the diagnosis of scleroderma and is not definitive in isolation. Autoantibody levels represent one parameter in a multicriterion diagnostic process.
Systemic rheumatic diseases are autoimmune disorders such as systemic lupus erythematosus, Sjögren's syndrome, scleroderma and rheumatoid arthritis. A general feature of systemic rheumatic diseases is the presence of circulating antibodies to a variety of cellular antigens. The detection and serological characterisation of specific autoantibodies plays an important role in the differential diagnosis of these diseases.
Antibodies to the Scl-70 autoantigen, also recognised as the enzyme Topoisomerase 1, are found in approximately 20% of scleroderma patients and are highly diagnostic of this disease. In the diffuse form of the disease, however, the frequency may be as high as 70%. This confirms the need for an accurate and easy-to-use test.
The wells of the microtitre strips are coated with affinity-purified Scl-70 antigen. During the first incubation, specific autoantibodies in diluted serum or plasma bind to the antigen-coated surface. The wells are then washed to remove unbound components. In the second incubation, the Conjugate, enzyme-labelled antibodies to human IgG, binds any surface-bound autoantibodies. After further washing, specific autoantibodies are traced by incubation with the Substrate. Addition of Stop Solution terminates the reaction, resulting in a coloured end-product. The amount of Conjugate bound is measured in absorbance units and compared with that bound by the Reference Control.