Detection of Smith antibodies, or anti-Sm, is very specific (99%) for systemic lupus erythematosus (SLE), thus regarded as a diagnostic marker for SLE. Detection of these autoantibodies is one of the ACR criteria for the diagnosis of SLE. However, a negative result does not rule out SLE.
There seems to be a relationship between the anti-Sm antibodies and severe organ manifestation of the disease (e.g. involvement of the CNS and/or kidney) and vascular skin and mucosal manifestations and the presence of antibodies against double-stranded DNA (dsDNA). Therefore anti-Sm is also regarded as a prognostic marker for lupus.
The anti-Sm antibody is part of the extractable nuclear antigen antibodies (ENA) panel, which is usually ordered following a positive antinuclear antibodies (ANA) test in people showing clinical signs of an autoimmune disease.
Evidence of anti-Sm antibodies can be provided by means of indirect immunofluorescence assays (IFA), by enzyme-linked immunosorbant assay (ELISA), or by line immunoassays (immunoblots). In indirect immunofluorescence assays on HEp-2 cells the interphase nuclei demonstrate a coarse granular pattern, whereas mitotic cells are negative.
Tests offered by ORGENTEC Diagnostika
Anti-Nuclear Antibodies HEp-2 (ANA-HEp-2) (ORG 870)