Among systemic lupus erythematosus–specific autoantibodies, which is highly specific but found in only about 30% of patients?

Among systemic lupus erythematosus–specific autoantibodies, which is highly specific but found in only about 30% of patients?

• A. Anti-Sm antibodies
• B. Anti-dsDNA antibodies
• C. Anti-Ro antibodies
• D. Anti-La antibodies

Answer: (A)

Some autoimmune markers in lupus are highly specific but not very sensitive: a positive result almost confirms lupus, but many patients don’t have it. Anti-Sm antibodies are the classic example of this pattern. They are highly specific for systemic lupus erythematosus—meaning you don’t see them much in other diseases—so a positive test strongly supports lupus. But they occur in only about a third of patients, so a negative result doesn’t rule out the disease. In contrast, other autoantibodies like anti-dsDNA are seen in more patients (higher sensitivity) though still helpful, while anti-Ro and anti-La are less specific to lupus and more common in other conditions like Sjögren’s syndrome. Therefore, anti-Sm antibodies fit the description of being highly specific but found in roughly 30% of patients.

Some autoimmune markers in lupus are highly specific but not very sensitive: a positive result almost confirms lupus, but many patients don’t have it. Anti-Sm antibodies are the classic example of this pattern. They are highly specific for systemic lupus erythematosus—meaning you don’t see them much in other diseases—so a positive test strongly supports lupus. But they occur in only about a third of patients, so a negative result doesn’t rule out the disease. In contrast, other autoantibodies like anti-dsDNA are seen in more patients (higher sensitivity) though still helpful, while anti-Ro and anti-La are less specific to lupus and more common in other conditions like Sjögren’s syndrome. Therefore, anti-Sm antibodies fit the description of being highly specific but found in roughly 30% of patients.