Sm (Smith) Antibody - IgG – BC289
🔬 Autoimmune Disease Marker (SLE)Report: Next day Evening (Except Sunday)
Sample Type: Blood (Serum)
Test Code: BC289
The Anti-Sm (Smith) Antibody test is a highly specific blood test used in the diagnosis of **Systemic Lupus Erythematosus (SLE)**, commonly known as Lupus. It detects IgG autoantibodies against Sm nuclear antigens, which are specific types of proteins found within the cell nucleus.
✔ A **highly specific marker** for the diagnosis of Systemic Lupus Erythematosus (SLE).
✔ Its presence strongly supports an SLE diagnosis, even if other markers are negative.
✔ Part of the ENA (Extractable Nuclear Antigen) panel, typically ordered following a positive ANA test.
✔ A simple, non-invasive blood test.
Anti-Sm: A Specific Fingerprint for Lupus (SLE)
Systemic Lupus Erythematosus (SLE) is a complex autoimmune disease where the immune system attacks various healthy tissues and organs throughout the body, including the skin, joints, kidneys, brain, heart, and lungs. Diagnosing SLE involves looking at a combination of clinical symptoms (like a butterfly rash, joint pain, fatigue, and organ involvement) and specific laboratory tests, particularly autoantibodies.
While the Antinuclear Antibody (ANA) test is a sensitive screening test for SLE (positive in most patients), it is not specific, meaning it can be positive in many other conditions. The Anti-Sm antibody test provides that crucial specificity. Autoantibodies against the Sm antigen (named after the first patient in whom it was identified, Stephanie Smith) are found almost exclusively in patients with SLE. Although only present in about 20-30% of SLE patients, finding Anti-Sm antibodies is considered one of the most specific laboratory markers for the disease.
Clinical Significance
A positive Anti-Sm antibody test result is a strong piece of evidence supporting an SLE diagnosis, often fulfilling one of the specific classification criteria used by rheumatologists. It helps differentiate SLE from other connective tissue diseases that might present with similar symptoms. While its presence doesn't typically correlate strongly with disease activity, it remains a highly reliable diagnostic marker.
Frequently Asked Questions (FAQ)
Systemic Lupus Erythematosus (SLE or Lupus) is a chronic autoimmune disease where the immune system attacks the body's own tissues, causing widespread inflammation and damage in organs like the skin, joints, kidneys, and brain.
The Anti-Sm antibody is highly specific for SLE. While not all Lupus patients have it (only 20-30%), its presence makes the diagnosis of SLE very likely, even if other tests are less clear.
The ANA test is a sensitive screening test but not specific (it can be positive in many conditions). The Anti-Sm test is part of a panel (ENA panel) ordered after a positive ANA to look for specific antibodies that help pinpoint the exact autoimmune disease, with Anti-Sm being highly specific for Lupus.
No. A negative Anti-Sm test does not rule out Lupus, as only about 20-30% of SLE patients test positive for this specific antibody. Your doctor will consider all your symptoms and other test results (like ANA, Anti-dsDNA, clinical criteria) to make a diagnosis.
No, fasting is not required for the Anti-Sm antibody blood test.