What this test measures
Anti-Scl-70 is an autoantibody directed against topoisomerase I — a nuclear enzyme that helps unwind DNA during cell division. The name "Scl-70" comes from "scleroderma 70 kDa antigen," from the size of the original antigen identified in the 1970s.
The test is a quantitative ELISA or line immunoassay reported as U/mL or as a positive/negative line on a strip. It is part of the extended ANA panel performed when a positive ANA shows a nucleolar or speckled-nucleolar pattern, or when scleroderma is suspected.
Why it matters
Anti-Scl-70 is highly specific (>95%) for systemic sclerosis (scleroderma) and is particularly associated with the diffuse cutaneous form — the more severe variant with widespread skin thickening, lung fibrosis (interstitial lung disease), and renal crisis. Early identification matters because scleroderma-related lung disease is the leading cause of death in this group, and early aggressive treatment (mycophenolate, nintedanib, tocilizumab) can slow progression.
In Indian rheumatology practice, anti-Scl-70 testing is routine in any patient with skin tightening (especially proximal to the MCP joints), Raynaud phenomenon with abnormal nailfold capillaries, unexplained pulmonary fibrosis, or unexplained pulmonary hypertension. Together with anti-centromere antibody (which suggests limited cutaneous scleroderma / CREST) and anti-RNA polymerase III (associated with rapid skin progression and renal crisis), anti-Scl-70 helps classify scleroderma into clinically meaningful subtypes that guide screening for end-organ disease.
How to prepare
No fasting required. Continue all medications including immunosuppressants and antifibrotic drugs — these do not affect antibody levels meaningfully.
Markers & reference ranges
Reference ranges below are typical adult values. Your lab's reported range may differ slightly based on the assay platform and patient demographics — always read your report against the range printed on it.
| Marker | Normal range | If low | If high |
|---|---|---|---|
| Anti-Scl-70 (Anti-Topoisomerase I) (U/mL or qualitative)[1][2][3] | Negative: < 20 U/mL (assay-dependent) | Negative does not rule out systemic sclerosis — about 70% of diffuse scleroderma patients are Scl-70 positive. Limited cutaneous scleroderma (CREST) is more often anti-centromere positive. | Positive anti-Scl-70 strongly supports diffuse systemic sclerosis. Associated with higher risk of interstitial lung disease (~60–70%), digital ulcers, and cardiac involvement. Higher titres correlate with more severe lung involvement. |
Scleroderma autoantibodies — clinical associations
| Antibody | Subtype | Key risk |
|---|---|---|
| Anti-Scl-70 (Topoisomerase I) | Diffuse cutaneous scleroderma | Interstitial lung disease, digital ulcers |
| Anti-Centromere | Limited cutaneous (CREST) | Pulmonary hypertension, slower skin progression |
| Anti-RNA Polymerase III | Diffuse cutaneous | Rapid skin progression, scleroderma renal crisis, malignancy |
| Anti-U3 RNP (fibrillarin) | Diffuse | Pulmonary hypertension, cardiac involvement |
| Anti-PM-Scl | Overlap (scleroderma + myositis) | Myositis, lung disease |
| Anti-Th/To | Limited | Pulmonary hypertension, lung fibrosis |
Frequently asked questions
Why has my rheumatologist ordered this test?
Usually because of Raynaud phenomenon with abnormal nailfold capillaries, skin tightening, unexplained reflux, or lung findings suggestive of scleroderma. It helps confirm the diagnosis and predict disease pattern.
Is anti-Scl-70 enough to diagnose scleroderma?
No single test diagnoses scleroderma. The 2013 ACR/EULAR criteria combine clinical findings (skin involvement, fingertip lesions, telangiectasia, abnormal capillaries) with autoantibodies. Anti-Scl-70 is highly supportive but the rheumatologist makes the final diagnosis.
Does positive Scl-70 always mean diffuse disease?
It strongly predicts diffuse cutaneous scleroderma but limited forms can rarely also be Scl-70 positive. Clinical examination drives the subtype call.
Will I definitely get lung disease?
Anti-Scl-70 positive patients have a high risk (~60–70% over time) of interstitial lung disease, so high-resolution CT chest and pulmonary function tests are recommended at baseline and periodically. Early-detected ILD is more treatable.
Do treatment medications lower the antibody?
Antibody levels stay relatively stable regardless of treatment. Doctors monitor disease using skin scores, lung function, echocardiogram, and clinical assessment — not by re-testing Scl-70.
Can anti-Scl-70 be negative even in confirmed scleroderma?
Yes — about 30% of diffuse scleroderma patients are Scl-70 negative; they may be positive for other scleroderma antibodies (RNA Pol III, U3-RNP, Th/To).
How long is the report?
Typically 2–3 days. Some labs use a scleroderma profile that includes Scl-70, anti-centromere, and anti-RNA Pol III together.
Related Autoimmune / Rheumatology tests
Tests commonly ordered alongside ANTI SCL - 70 ANTIBODY, or that help interpret an unexpected result.
Sources & references
- NCBI StatPearls — Scleroderma · accessed 2026-05-30T00:00:00.000Z
- NIH MedlinePlus — Scleroderma · accessed 2026-05-30T00:00:00.000Z
- ACR/EULAR — 2013 Systemic Sclerosis Classification Criteria · accessed 2026-05-30T00:00:00.000Z
- Mayo Clinic Labs — Scl-70 Antibody · accessed 2026-05-30T00:00:00.000Z
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