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Smith Extractable Nuclear Antibody Blood Test

Last updated Oct. 12, 2015

The Smith Extractable Nuclear Antibody Blood Test helps detect anti-Sm antibodies in cells. It is used to diagnose systemic lupus erythematosus (or lupus)


What are the other Names for this Test? (Equivalent Terms)

  • Anti-Sm Antibodies Blood Test
  • Sm Antibodies Blood Test
  • Smith Extractable Nuclear Ab Blood Test

What is the Smith Extractable Nuclear Antibody Blood Test? (Background Information)

  • Smith, or Sm, antibodies are associated with an autoimmune disorder called systemic lupus erythematosus (SLE). They are used to identify SLE
  • Antibodies are bodily defense proteins that recognize foreign invaders, such as bacteria. They interact with the immune system and initiate an immune response to eliminate the body of the invader
  • Autoantibodies are antibodies that mistakenly recognize the body’s own cells and cellular components as foreign invaders. Autoantibodies against Sm, a protein inside the nuclei (plural for nucleus) in cells, are indicative of systemic lupus erythematosus
  • SLE can affect any number of organs, including the kidneys, heart, lungs, skin, and brain. It is characterized by inflammation as a result of autoantibodies attacking cells in these organs
  • The Smith Extractable Nuclear Antibody Blood Test helps detect anti-Sm antibodies in cells. It is used to diagnose systemic lupus erythematosus (or lupus)

There are 4 techniques for detecting anti-Sm antibodies:

  • Enzyme-linked immunosorbent assay (ELISA) - uses enzymes linked to color-producing molecules to identify a compound
  • Counter immunoelectrophoresis (CIE) - uses an electrical field and antibody-target precipitation to identify a compound
  • Immunodiffusion - similar to CIE, but does not employ an electric field
  • Hemagglutination - uses red blood cells and clumping caused by binding to identify a compound

What are the Clinical Indications for performing the Smith Extractable Nuclear Antibody Blood Test?

Following are the clinical indications for performing the Smith Extractable Nuclear Antibody Blood Test:

  • Monitoring the progress of lupus
  • Following up to a positive test for antinuclear antibody (ANA)
  • Differentiating lupus from other autoimmune disorders
  • Fatigue
  • Joint pain
  • Fever
  • Rash
  • Chest pain
  • Dry eyes
  • Headache
  • Altered mental status
  • Hair and weight loss
  • Skin sensitivity to light
  • Abnormalities in urination and the urine produced, including dark urine

How is the Specimen Collected for Smith Extractable Nuclear Antibody Blood Test?

Following is the specimen collection process for Smith Extractable Nuclear Antibody Blood Test:

Sample required: Blood

Process of obtaining blood sample in adults:

  • A band is wrapped around the arm, 3-4 inches above the collection site (superficial vein that lies within the elbow pit)
  • The site is cleaned with 70% alcohol in an outward spiral, away from the zone of needle insertion
  • The needle cap is removed and is held in line with the vein, pulling the skin tight
  • With a small and quick thrust, the vein is penetrated using the needle
  • The required amount of blood sample is collected by pulling the plunger of the syringe out slowly
  • The wrap band is removed, gauze is placed on the collection site, and the needle is removed
  • The blood is immediately transferred into the blood container, which has the appropriate preservative/clot activator/anti-coagulant
  • The syringe and the needle are disposed into the appropriate “sharp container” for safe and hygienic disposal

Preparation required: No special preparation is needed prior to the test.

What is the Significance of the Smith Extractable Nuclear Antibody Blood Test Result?

The significance of the Smith Extractable Nuclear Antibody Blood Test result is explained:

  • A positive test may indicate systemic lupus erythematosus (SLE) in 20% of cases
  • A negative test does not necessarily rule out SLE; the condition may still be present in 80% of the cases

The laboratory test results are NOT to be interpreted as results of a "stand-alone" test. The test results have to be interpreted after correlating with suitable clinical findings and additional supplemental tests/information. Your healthcare providers will explain the meaning of your tests results, based on the overall clinical scenario.

Additional and Relevant Useful Information:

Other tests often performed alongside the Smith Extractable Nuclear Antibody Blood Test include:

  • Antinuclear antibody blood test
  • Anti-dsDNA antibody blood test
  • Anti-U1RNP blood test
  • Anti-Ro/SSA and anti-La/SSB antibody blood test
  • Serum complement blood test
  • Anti-histone antibodies blood test

Certain medications that you may be currently taking may influence the outcome of the test. Hence, it is important to inform your healthcare provider of the complete list of medications (including any herbal supplements) you are currently taking. This will help the healthcare provider interpret your test results more accurately and avoid unnecessary chances of a misdiagnosis.

What are some Useful Resources for Additional Information?

  • Systemic lupus erythematosus (SLE or Lupus) is an autoimmune disorder that may affect any area of the body such as the skin, joints, blood cells, kidneys, brain, heart, and lungs

The following article link will help you understand systemic lupus erythematosus:

http://www.dovemed.com/diseases-conditions/systemic-lupus-erythematosus/ 

Please visit our Laboratory Procedures Center for more physician-approved health information:

http://www.dovemed.com/common-procedures/procedures-laboratory/ 

References and Information Sources used for the Article:

Lab Tests Online (2014, March 31). Retrieved September 5, 2015 from http://labtestsonline.org/understanding/analytes/ena-panel/

Martini, F., Nath, J. L., & Bartholomew, E. F. (2012). Fundamentals of anatomy & physiology (9th ed.). San Francisco: Benjamin Cummings.

The Johns Hopkins Lupus Center. (2015). Lupus blood tests. Retrieved from http://www.hopkinslupus.org/lupus-tests/lupus-blood-tests/

Reviewed and Approved by a member of the DoveMed Editorial Board
First uploaded: Sept. 13, 2015
Last updated: Oct. 12, 2015