Intended use

The DIASTAT^? anti-dsDNA test is a quantitative/qualitative enzyme-linked immunosorbent assay (ELISA) for the detection of IgG and IgM autoantibodies specific for double-stranded DNA (dsDNA) in human serum or plasma. It is intended to aid in the diagnosis of systemic lupus erythematosus, and to monitor dsDNA antibody levels during treatment and remission. Autoantibody levels represent one parameter in a multicriterion diagnostic process.

Background

Systemic rheumatic diseases are autoimmune disorders such as systemic lupus erythematosus (SLE), rheumatoid arthritis and mixed connective tissue disease. 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 against dsDNA are highly specific for SLE and are detected at a high frequency in untreated patients with active disease. The presence of dsDNA antibodies in SLE is one of the criteria for disease classification by the American College of Rheumatology. Several investigators have reported a correlation between disease activity and fluctuations in antibody levels, consequently the monitoring of dsDNA activity is considered of use in the management of SLE patients.

A number of techniques are available for detecting dsDNA autoantibodies, including Farr radioimmunoassay and the Crithidia luciliae immunofluorescence assay. These tests have inherent drawbacks in complexity, lack of sensitivity and reproducibility. ELISAs offer simplicity, sensitivity, reproducibility and objectivity over other methods and can be standardised by reference to the World Health Organisation (WHO) anti-dsDNA standard, Wo/80.
 

Technical information

The wells of the microtitre strips are coated with a preparation of calf thymus selected for its high dsDNA content. 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 and IgM, 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. In the qualitative protocol, the amount of Conjugate bound by the sample is compared with that bound by the Reference Control. In the quantitative protocol, the concentration of anti-dsDNA autoantibody can be estimated by interpolation from a dose-response curve based on Standards. The Standards are referenced against WHO Reference Preparation Wo/80 and reported in International units per mL (IU/mL).