Intended use

The DIASTAT® ENA Single Well Screen is a qualitative enzyme-linked immunosorbent assay (ELISA) for the simultaneous detection of the IgG class of autoantibodies specific for Sm, RNP, Ro (SS-A), La (SS-B), Scl-70 and Jo-1 in human serum or plasma. It detects the presence of autoantibodies but does not define the specificity. The test is intended to screen out samples that are negative for antibodies to these extractable nuclear antigens and is not definitive in isolation. Positive samples should be tested further to identify the specific autoantibodies present.

Background

A general feature of systemic rheumatic disease is the presence of circulating antibodies to a variety of cellular antigens such as extractable nuclear antigens (ENAs). The detection of specific antibodies to ENAs plays an important role in the differential diagnosis of systemic rheumatic diseases such as systemic lupus erythematosus (SLE) and lupus variants, scleroderma, mixed connective tissue diseases (MCTD), Sjögren’s syndrome, CREST, polymyositis and rheumatoid arthritis. Positive samples should be tested to determine the specific autoantibody profile using DIASTAT® kits for the quantitative/qualitative determination of anti-Sm, anti-Sm/RNP, anti-Ro (SS-A), anti-La (SS-B), and the qualitative determination of anti-Scl-70 and anti-Jo-1.

Sm is a non-histone glycoprotein and antibodies against this extractable nuclear antigen are specific serological markers of SLE.

U1-RNP is a ribonucleoprotein; antibodies against it are found in several connective tissue diseases, principally SLE (30?40%) and MCTD (>95%). MCTD presents a combination of clinical features, which may also be seen in SLE, polymyositis and scleroderma. Although antibodies to dsDNA, Sm and Ro are infrequently found in MCTD, high titres of anti-RNP antibodies are usually considered diagnostic of the disease.

Ro (SS-A) and La (SS-B) are RNA-protein complexes; antibodies against them are found in Sjögren’s syndrome (60% and 40% respectively), SLE (30% and 15%), scleroderma and neonatal lupus erythematosus. There is evidence associating these antibodies to particular clinical characteristics, and with congenital heart block.

The Scl-70 antigen is also recognised as the enzyme Topoisomerase 1; autoantibodies against this enzyme are found in approximately 20% of scleroderma patients and are highly diagnostic of this disease. In the diffuse form of the disease the frequency may be as high as 70%.

The Jo-1 antigen is also recognised as the enzyme histidyl-t RNA synthetase; autoantibodies against this enzyme are found in approximately 25% of polymyositis patients. High proportions of patients with interstitial lung disease, associated with polymyositis, are also positive for the antibody.

Technical Information

The wells of the microtitre strips are coated with a mixture of six affinity-purified antigens. 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 appropriate Reference Control.