Enzyme Immunoassay for the Detection of autoantibodies to Sm in Human Serum.

Autoimmunity is characterized by the presence of antinuclear antibodies (ANA) against a multitude of macromolecules. Specific combinations of circulating ANA are the distinctive features of the different types of autoimmune diseases. Therefore, identification of specific autoantibodies is important in the diagnosis and treatment of the autoimmune disease.

The Smith (Sm) antigen is a non-histone nuclear antigen comprised of small nuclear RNAs, U1, U2, U4, U5, and U6 (4-6). Antibodies to Sm are present in sera of approximately 40% of systemic lupus erythematosus (SLE) patients. These antibodies have also not been associated with other autoimmune diseases such as rheumatoid arthritis and Sjogren's syndrome, and therefore, serve as specific diagnostic markers of SLE. Double diffusion and hemagglutination have been predominant methods of choice for the detection of anti-Sm antibodies; however, these techniques have reportedly failed to detect anti-Sm antibodies in greater than 50% of confirmed cases. Comparative studies have shown that enzyme immunoassays (EIA) are more reliable methods for the detection of serum anti-Sm antibodies. The Micro Detect anti-Sm Test is an enzyme-linked immunosorbent assay, which in contrast to other methods has the advantages of short incubations times, increased sensitivity, and specificity.

SUMMARY OF 510 (k)

MDI Sm Test reagents (P/N: SmKi-G) are intended for the semi-quantitative determination of IgG antibodies to Sm in human serum. The principal diagnostic value of this test is detection of autoantibodies, which are used as an aid in patients with rheumatoid diseases. The Micro Detect, Inc. Sm reagent (MDI Sm Test) is intended to be used as a manual procedure. The reagents are supplied as a micro plate coated with specific antigens and Controls, Wash Buffer, Sample Diluent, Conjugate, Substrate, and Stop Solution. The patient results obtained using the MDI Sm Test is substantially equivalent to those obtained by using predicate assays:

Relative Sensitivity: 100%

Relative Specificity: 100 %

Precision (%CV): 3.7-7.07 (Inter) and 1.06- 7.3 (Intra)

Stability: One year at 2-8 C. The stability of the MDI Sm Test Kit for the detection of IgG antibodies to Sm was found to be one year at 2-8 C. This was predicted from studies done under stress condition (37 C). Real time stability has only been monitored for two weeks at 2-8 C.

The MDI Sm Test system is shown to be safe and effective and provide results, which are substantially equivalent to those, obtained by predicate products.