Sm Ab ELISA Kit (Smith Antibodies)

Full Name: Sm Ab ELISA Kit (Smith Antibodies)
Reactivity: Human
Sample Type: Serum, Plasma
Sensitivity: 1.0 U/ml


Anti-Smith (Sm) antibodies are a specific type of immunoglobulin that target small nuclear ribonucleoproteins (snRNP). These antibodies are associated with systemic lupus erythematosus (SLE) and mixed connective-tissue disease (MCTD). These are immunoglobulins, which are Y-shaped proteins produced by the immune system in response to foreign substances. They specifically target the Sm proteins, which are part of the snRNP complex. The snRNP complex, including the Sm proteins, plays a crucial role in the processing of messenger RNA (mRNA)

Anti-Smith antibodies can disrupt the normal function of the snRNP complex, leading to immune system dysregulation and the development of autoimmune diseases like SLE. They are an important component of the classification criteria for SLE. However, they lack sensitivity and are not present in all SLE cases. Approximately 30% of SLE cases and 8% of MCTD cases show elevated levels of anti-Smith antibodies.

There is no defined test prescribed for screening anti-Smith reactivity in patients with SLE. Commonly used tests include indirect immunofluorescence tests (IIFT) and antigen-specific immunoassays. These tests help identify the presence of anti-Smith antibodies in patient samples. Anti-Smith antibodies are highly specific for SLE, but their presence alone is not sufficient for a diagnosis.


Human Sm Ab ELISA kit can be used for analysing in-vitro quantitative levels of IgG auto-antibodies to Smith antibodies (Sm Ab, anti-Sm IgG, anti-Sm antibody) using human serum and plasma. This assay has a minimum analytical sensitivity limit of 1.0 U/ml.


All reagents supplied need to be stored at 2 °C – 8 °C, unopened reagents will retain reactivity until expiration date. Do not use reagents beyond this date.

  • Divisible Microplate: Consisting of 12 modules of 8 wells, highly purified Smith antibody bound to microwells.
  • Calibrators (A-F): Concentration 0-200 U/ml, made up from Sm antibodies.
  • Controls Positive and Control Negative: Containing human Sm antibody.
  • Sample Buffer (5x).
  • Enzyme Conjugate: Contains anti-human IgG antibodies, HRP labelled.
  • TMB Substrate.
  • Stop Solution: Contains acid.
  • Wash Buffer (50x Concentrated).
  • Instruction Manual.
  • Certificate of Analysis.


The minimum detection sensitivity level of human IgG against Smith antibodies (Sm antibody, Sm Ab, anti-Sm IgG) using current Sm Ab ELISA kit was 1.0 U/ml. The dynamic range for this assay is 12.5 – 200.0 U/ml.


– Measuring Range: 0 – 200 U/ml
– Linearity: 97 – 100%
– Limit Of Detection (LOD): 1 U/ml.
– Results Interpretation: Negative: < 15 U/ml, Borderline 15-25 U/ml, Positive: ≥ 25 U/ml.
– Expected Values: Cut-off 25 U/ml.
– Intra Assay: 2.0 – 4.1%
– Inter Assay: 1.3 – 5.3%
– Interference: None.
– Clinical Diagnosis: Sensitivity (51.4%), Specificity (95.8%), Overall agreement (79.5%).


  1. Association of cerebrospinal fluid anti-Sm antibodies with acute confusional state in systemic lupus erythematosus. Arthritis Res Ther. (2014) 16 (5): 450. Hirohata S., et al.
  2. Sm peptides in differentiation of autoimmune diseases. Adv Clin Chem. (2011) 54: 109-28. Review. Mahler M.
  3. Clinical value of an integrated ELISA system for the detection of 6 autoantibodies (ssDNA, dsDNA, Sm, RNP/Sm, SSA, and SSB). J Rheumatol. (1990) 17 (2): 192-200. Froelich C.J., et al.
  4. Diagnostic criteria for systemic lupus erythematosus: a critical review. J Autoimmun. (2014) 48-49: 10-3. Review. Yu C., et al.
  5. Anti-Sm and anti-RNP antibodies. Autoimmunity. (2005) 38 (1): 47-54. Review. Migliorini P., et al.
  6. The sensitivity and specificity of autoantibodies to the Sm_antigen in the diagnosis of systemic lupus erythematosus. Ann Acad Med Singapore. (1998) 27 (1): 21-3. Pan L.T., et al.


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