What is the common initial serologic screen for suspected SLE?

• A. ANA
• B. Anti-dsDNA
• C. Anti-Smith Ab
• D. RF

Answer: (A)

Antinuclear antibody testing is used as the initial screen for suspected SLE because it is highly sensitive. Most patients with SLE have ANA positivity, so a negative result makes SLE unlikely. A positive ANA, however, is not specific to SLE and can occur in other autoimmune diseases and even in healthy people. When ANA is positive, more specific tests are pursued to confirm diagnosis and assess activity, such as anti-dsDNA and anti-Smith antibodies. Anti-dsDNA often correlates with disease activity and lupus nephritis, while anti-Smith is highly specific but less sensitive. RF is associated with rheumatoid arthritis and isn’t used to screen for SLE.