What Is the SCL-70 Antibody Test?
The SCL-70 antibody test is a blood test used to detect antibodies against topoisomerase I, an enzyme found in the nucleus of cells. These antibodies are part of the antinuclear antibody (ANA) family and are often associated with certain autoimmune conditions—most notably systemic sclerosis (scleroderma).
This test helps doctors evaluate symptoms such as skin thickening, joint pain, fatigue, or shortness of breath that may be related to autoimmune diseases.
Reference Range:
< 1.0 AI (Antibody Index) — Negative
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<1.0 AI: Negative (normal)
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1.0–1.5 AI: Borderline
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>1.5 AI: Positive (elevated antibody levels)
AI (Antibody Index) is a standardized unit that reflects the strength or concentration of antibodies in the blood.
What Does a Positive or Elevated SCL-70 Antibody Mean?
A positive SCL-70 antibody result (AI ≥ 1.0) may indicate an autoimmune response, particularly:
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Systemic sclerosis (diffuse scleroderma) – a chronic autoimmune disease that causes hardening and tightening of the skin and can affect internal organs like the lungs and kidneys.
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The presence of SCL-70 antibodies is most strongly linked to the diffuse cutaneous form of scleroderma and may correlate with lung involvement (pulmonary fibrosis).
However, a positive result does not confirm a diagnosis on its own. It must be interpreted alongside clinical symptoms, physical examination, and other tests (like ANA, anti-centromere antibodies, and imaging).
What Does a Negative SCL-70 Antibody Result Mean?
A result below 1.0 AI is considered negative, suggesting that SCL-70 antibodies were not detected in the blood. This lowers the likelihood of systemic sclerosis but does not completely rule out autoimmune disease, as other antibodies may be involved.
When Is This Test Ordered?
Your healthcare provider may order the SCL-70 antibody test if you’re experiencing symptoms such as:
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Thickened or tight skin
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Raynaud’s phenomenon (fingers turning white or blue in cold)
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Joint or muscle pain
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Shortness of breath or signs of lung involvement
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Fatigue or gastrointestinal symptoms
In summary, the SCL-70 antibody test is a valuable tool in diagnosing and monitoring systemic sclerosis, especially its diffuse form. A positive result warrants further evaluation by a rheumatologist to determine the underlying cause and appropriate treatment.
SCL-70 Antibody
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