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Diagnostic Tests – ANA, Anti–Double-Stranded DNA (anti–dsDNA), and Anti-Smith (anti-Sm) Antibodies
1. What diseases are they associated with?
These antibodies are classically associated with systemic lupus erythematosus (SLE), with different roles in screening versus confirmation:
2. When do you answer ANA, anti-dsDNA, and anti-Sm?
You should select this antibody panel when a clinical vignette suggests systemic lupus erythematosus, especially in:
High-yield exam pearl:
If you want, I can also create a JPEG comparison diagram (ANA vs dsDNA vs anti-Sm) like your other rheumatology visuals.
1. What diseases are they associated with?
These antibodies are classically associated with systemic lupus erythematosus (SLE), with different roles in screening versus confirmation:
- ANA (Antinuclear Antibody)
- >98% sensitive for SLE
- Not specific
- A negative ANA essentially rules out SLE (≈98% negative predictive value)
- Anti–double-stranded DNA (anti–dsDNA)
- Highly specific (~99%) for SLE
- Often correlates with disease activity, especially lupus nephritis
- Anti-Smith (anti-Sm)
- Extremely specific for SLE
- Lower sensitivity, but when present, it is diagnostic
2. When do you answer ANA, anti-dsDNA, and anti-Sm?
You should select this antibody panel when a clinical vignette suggests systemic lupus erythematosus, especially in:
- A young woman
- Rash (e.g., malar rash, photosensitivity)
- Arthralgias or arthritis
- History of multiple spontaneous abortions (suggesting lupus anticoagulant / antiphospholipid syndrome)
High-yield exam pearl:
- Suspected SLE → ANA first
- Confirm SLE → anti-dsDNA and anti-Sm
- Negative ANA → SLE is essentially excluded
If you want, I can also create a JPEG comparison diagram (ANA vs dsDNA vs anti-Sm) like your other rheumatology visuals.
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