Systemic Lupus Erythematosus Quiz

See Investigations. Option E is correct. Anti-nuclear antibodies (ANA) are autoantibodies against components of the cell nucleus, and they are present in up to about 95% of patients with SLE. That makes the ANA test the most sensitive test for lupus: sensitivity is the proportion of people with a disease who test positive. A highly sensitive test is good at ruling a disease out, so a negative ANA makes lupus unlikely, and for this reason it is used as the screening test. However, ANA is not specific. Specificity is the proportion of people without the disease who test negative, and ANA is also positive in other connective tissue diseases, such as systemic sclerosis, and in some healthy people, so a positive result alone cannot make the diagnosis. A positive ANA is therefore followed by more specific tests such as anti-double-stranded DNA and anti-Smith antibodies, and the result is always read together with the symptoms and examination. A memory aid for screening tests is SnNOut: a Sensitive test, when Negative, rules the disease Out.

• Test: ANA are autoantibodies against the cell nucleus, present in up to about 95% of patients with SLE
• Sensitivity: very high, so a negative result makes lupus unlikely (SnNOut)
• Specificity: low, because ANA is also positive in other diseases and in healthy people, so a positive result needs more specific tests