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Diagnostic Tests – Anti–Scl-70 (Anti–Topoisomerase I) Antibodies
1. What is this?
Anti–Scl-70 antibodies are autoantibodies directed against topoisomerase I, a nuclear enzyme. They are associated with systemic sclerosis, particularly the diffuse cutaneous form. Their presence supports the diagnosis and helps with risk stratification.
2. When do you answer anti–Scl-70 antibodies?
Order anti–Scl-70 when the clinical picture suggests diffuse systemic sclerosis, such as:
Exam pearl: Diffuse scleroderma features → think anti–Scl-70.
3. How would a negative test affect management?
A negative anti–Scl-70 does not rule out systemic sclerosis because the test has low sensitivity (~30%).
If clinical suspicion remains high, management and further evaluation should continue despite a negative result.
4. What is the patient at risk for if anti–Scl-70 is positive?
A positive anti–Scl-70 is most strongly associated with severe pulmonary involvement, especially:
This finding signals a higher-risk disease course and warrants close pulmonary monitoring.
High-yield contrast
1. What is this?
Anti–Scl-70 antibodies are autoantibodies directed against topoisomerase I, a nuclear enzyme. They are associated with systemic sclerosis, particularly the diffuse cutaneous form. Their presence supports the diagnosis and helps with risk stratification.
2. When do you answer anti–Scl-70 antibodies?
Order anti–Scl-70 when the clinical picture suggests diffuse systemic sclerosis, such as:
- Polyarthralgia
- Raynaud phenomenon
- Thick, tight (“hide-bound”) skin
- Dysphagia and GI hypomotility
- Evidence of pulmonary and/or renal involvement
Exam pearl: Diffuse scleroderma features → think anti–Scl-70.
3. How would a negative test affect management?
A negative anti–Scl-70 does not rule out systemic sclerosis because the test has low sensitivity (~30%).
If clinical suspicion remains high, management and further evaluation should continue despite a negative result.
4. What is the patient at risk for if anti–Scl-70 is positive?
A positive anti–Scl-70 is most strongly associated with severe pulmonary involvement, especially:
- Interstitial lung disease
- Pulmonary fibrosis
This finding signals a higher-risk disease course and warrants close pulmonary monitoring.
High-yield contrast
- Limited systemic sclerosis (CREST) → Anticentromere antibodies
- Diffuse systemic sclerosis → Anti–Scl-70 antibodies
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