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Sm/RNP Antibody Blood Test

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The Sm/RNP Antibody test measures the Smith and RNP antibodies in the blood to help diagnose mixed connective tissue disease (MCTD), lupus, and scleroderma.


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Test Code:


CPT Code(s):



Immunoassay (IA)




No special preparation is required.

Test Results:

3-7 days. May take longer based on weather, holiday, or lab delays.

Walk-In Lab is prohibited from selling Quest tests to residents in the following states:AZ, NY, NJ, RI

This test measures the Smith and RNP antibodies in the blood to diagnose mixed connective tissue disease (MCTD), lupus, and scleroderma. In addition, this test helps to determine if an individual may have another autoimmune disease with similar symptoms.

MCTD, lupus, and scleroderma are autoimmune diseases that cause chronic inflammation in the skin and other body parts. Lupus is typically more widespread and causes severe tissue damage in organs. However, MCTD is a rare overlapping disorder that may cause individuals to experience a combination of symptoms of multiple autoimmune diseases.

Each of these disorders is characterized by two types of antibodies: Smith (Sm) Antibody and Ribonuclear Protein (RNP) Antibody. These antibodies are produced when a person's immune system attacks its cells or tissues. This attack can cause inflammation, tissue damage, and other signs and symptoms related to an autoimmune disease.

Although, signs and symptoms of autoimmune diseases may vary and affect different body parts. They may include:

  • Depression
  • Fever and chronic fatigue
  • Hair loss
  • Hemolytic anemia
  • High levels of protein in the urine
  • Joint swelling, stiffness, or pain
  • Muscle pain or weakness
  • Seizures
  • Sensitivity to light
  • Skin rashes or sores

Individuals may order this test if they have signs or symptoms of MCTD, lupus, scleroderma, or other autoimmune diseases. Furthermore, this test may help diagnose or monitor an autoimmune disorder's activity or progression.

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