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Anti-Smith Antibody 

  • Author: Niral M Patel; Chief Editor: Eric B Staros, MD  more...
Updated: Apr 25, 2013

Reference Range

Anti-Smith antibodies are present in some cases of systemic lupus erythematosus (SLE) and mixed connective-tissue disease (MCTD).

The reference range of anti-Smith antibodies is negative.



Anti-Smith antibody has low sensitivity but high specificity for systemic lupus erythematosus (SLE). It is occasional present in mixed connective-tissue disease (MCTD).

Anti-Smith antibody levels are elevated in 30% of SLE cases and 8% of MCTD cases[1]

Anti-Smith antibody is more common in blacks and Asians with SLE than in whites with SLE.[2] Elevated anti-Smith levels persist even after anti-DNA levels have returned to the normal range. This is useful when testing a patient with decreased signs or symptoms of SLE (ie, a waning phase).

Sensitivities and specificities vary by laboratory technique. Immunoblotting and immunoprecipitation are very sensitive. Immunodiffusion, passive hemagglutination, and counterimmunoelectrophoresis are not as sensitive.[3]



See the list below:

  • There are no special collection conditions or timings.
  • A standard red-top tube is used
  • Hemolysis and lipemia should not affect the results but should be avoided, if possible.
  • There are no special storage conditions.
  • Anti-Smith antibody testing is usually not part of a laboratory panel.



Anti-Smith antibodies are present in some cases of systemic lupus erythematosus (SLE) and mixed connective-tissue disease (MCTD). Smith antigens are part of the extractable nuclear antigens (ENAs); specifically, they are the proteins that are resistant to ribonuclease. Ribonucleoproteins, the other part of ENAs, are ribonuclease susceptible.[4]

Smith antigens, along with RNP antigens, are part of small nuclear RNAs. levels of antibodies to these two antigens are often elevated in SLE. The Smith antigen is composed of the B1, D, and E proteins.[3]


Anti-Smith antibody testing should be considered in patients with signs or symptoms of SLE or MCTD, such as the following:

  • Malar rash
  • Discoid rash
  • Photosensitivity
  • Mucosal ulcers
  • Avascular necrosis
  • Anemia
  • Arthritis/arthralgia
  • Serositis
  • Glomerulonephritis
Contributor Information and Disclosures

Niral M Patel St Louis University School of Medicine

Niral M Patel is a member of the following medical societies: American Academy of Emergency Medicine, American College of Physicians, American Medical Association

Disclosure: Nothing to disclose.

Chief Editor

Eric B Staros, MD Associate Professor of Pathology, St Louis University School of Medicine; Director of Clinical Laboratories, Director of Cytopathology, Department of Pathology, St Louis University Hospital

Eric B Staros, MD is a member of the following medical societies: American Medical Association, American Society for Clinical Pathology, College of American Pathologists, Association for Molecular Pathology

Disclosure: Nothing to disclose.

  1. Mosby’s Diagnostic and Laboratory Test Reference 9th Edition ISBN: 9780323053457 (p.77-78).

  2. Wallach’s Interpretation of Diagnostic Tests 9th Edition ISBN: 9781605476674 (p.61-62).

  3. Henry’s Clinical Diagnosis and Management by Laboratory Methods 21st Edition (p. 919).

  4. Kelley's Textbook of Rheumatology, 9th ed.

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