Anti-Scl-70 (Topoisomerase I) Antibody

Antibodies against an enzyme called topoisomerase I. A positive result is linked to systemic sclerosis (scleroderma), especially the diffuse form of the disease.

AI-verified against cited sources. Awaiting expert reviewAlso called Scl-70, anti-Scl-70, anti-topo ILOINC 47322-3

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What it is

Scl-70 is another name for topoisomerase I, an enzyme that helps copy and read DNA. In systemic sclerosis, also called scleroderma, the immune system can make antibodies against it. This test measures those antibodies in your blood. Labs use methods such as multiplex bead assays or ELISA, and each reports in its own units with its own cutoff.

Why it matters

Anti-Scl-70 is one of three antibodies counted in the 2013 ACR/EULAR classification criteria for systemic sclerosis, where any of them adds 3 points. More than half of people with the disease have one of the three. Anti-Scl-70 alone is found in about 1 in 5, and it is linked to the diffuse form of the disease and to scarring of the lungs. It also shows up in some people with other autoimmune conditions, so a positive result is read together with symptoms and other tests.

If it’s high

A result above your lab's cutoff is reported as positive. It is linked to systemic sclerosis and, within that condition, to the diffuse skin form and lung involvement. It is not a diagnosis by itself. Positive results are also reported in some people with lupus, and false positives can happen. Your clinician reads the result with your symptoms, an ANA test and other antibodies.

Common causes

A false-positive result, which can happen when DNA in the test kit or DNA bound to antibodies in your blood sticks to the Scl-70 antigen, especially in people who also have anti-dsDNA antibodies
Lupus or another autoimmune condition, since Scl-70 antibodies are reported in a varying share of people with lupus
Systemic sclerosis (scleroderma), especially the diffuse form

What can help

Ask how this result fits with your symptoms, such as thickened skin on the fingers, fingers that turn white or blue in the cold, or shortness of breath
Ask whether other scleroderma-related antibodies (anticentromere, anti-RNA polymerase III) or lung tests are needed
Ask whether a result near the cutoff should be confirmed with another method

Usual ranges

What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.

For adults: 0–29 AU/mL. Source: ARUP Laboratories, UI Health Care (University of Iowa Hospitals & Clinics) Laboratory Services Handbook.

Adults (this one applies)0–29 AU/mL
Sources: ARUP Laboratories, UI Health Care (University of Iowa Hospitals & Clinics) Laboratory Services Handbook

What can affect your result

Test method: bead assays, ELISA and other immunoassays use different scales and cutoffs
Anti-dsDNA antibodies and DNA contamination of the test antigen can cause false positives
Other autoimmune conditions: some people with lupus test positive
A negative result does not rule out systemic sclerosis, because other antibodies can be present
Anti-dsDNA antibodies, and DNA contamination of the test antigen, can cause false-positive results (ARUP).
Kits differ: ARUP uses a multiplex bead assay, and other labs use ELISA or other immunoassays with their own scales and cutoffs.
ARUP rejects plasma, other body fluids, and contaminated, hemolyzed or severely lipemic samples for this test.

When to talk to a clinician

A positive Scl-70 result is not an emergency by itself. Talk with a clinician soon if you have it along with thickened or tight skin on the fingers, fingers that turn white or blue in the cold, sores or pitting scars on the fingertips, or a new cough or shortness of breath. Call 911 or your local emergency number for severe trouble breathing.

Questions you could ask

Which other antibodies or tests would help explain my symptoms?
What do my symptoms and other antibody tests say about this result?
Do I need lung tests?
Could this be a false positive, and should it be confirmed with another method?

Questions people ask

Does a positive Scl-70 mean I have scleroderma?

Not by itself. It is strongly linked to systemic sclerosis and counts toward its classification criteria, but it is also reported in some people with lupus, and false positives happen. Your clinician looks at your symptoms, an ANA test and other antibodies.

Can I have scleroderma with a negative Scl-70?

Yes. Scl-70 alone is found in about 1 in 5 people with systemic sclerosis. Other antibodies, such as anticentromere or anti-RNA polymerase III, go with other forms of the disease, and some people have none of them.

What do AU/mL results mean?

AU/mL stands for arbitrary units per mL. Each lab's kit has its own scale and cutoff, so a number from one lab cannot be compared with a number from another. At one large reference lab, 29 or less is negative and 41 or more is positive.

Show the science and sources

For clinicians and researchers

Anti-Scl-70 antibodies (anti-topoisomerase I, ATA, anti-topo I) are autoantibodies against topoisomerase I, a DNA-binding enzyme. They are one of three SSc-related antibodies in the 2013 ACR/EULAR classification criteria, with anticentromere and anti-RNA polymerase III antibodies, where any one of them scores 3 points toward a threshold of 9 (ARUP Consult citing van den Hoogen 2013). In the validation sample the criteria had sensitivity 0.91 and specificity 0.92 (PubMed abstract). More than half of patients with SSc have one of the three antibodies, which are generally exclusive of each other, and Scl-70 alone is detected in about 20% (ARUP). Anti-topo I is associated with diffuse skin involvement and pulmonary fibrosis, and with a poorer prognosis and SSc-related mortality, whereas anticentromere antibodies go with limited cutaneous disease (J Dermatol 2010). Anti-Scl-70 has been reported in a varying percentage of people with SLE. ARUP warns that anti-DNA/DNA complexes in SLE sera may bind topoisomerase I and that DNA contamination of recombinant antigen can cause false positives, and advises strong clinical correlation if both Scl-70 and dsDNA antibodies are detected. ARUP's multiplex bead assay reports AU/mL (29 or less negative, 30 to 40 equivocal, 41 or more positive; reference interval 40 or less). A negative result does not exclude SSc, and ARUP suggests testing for centromere, RNA polymerase III, U3-RNP, PM/Scl or Th/To antibodies if suspicion remains. Units and cutoffs are assay-specific.

LOINC 47322-3 (primary), 26975-3, 27416-7, 8092-9. Specimen: serum.

Sources

Scleroderma (Scl-70) (ENA) Antibody, IgG (test 0050599), ARUP Laboratories
Systemic Sclerosis, ARUP Consult
2013 classification criteria for systemic sclerosis: an American College of Rheumatology/European League against Rheumatism collaborative initiative, Arthritis & Rheumatism (2013)
Autoantibody profiles in systemic sclerosis: predictive value for clinical evaluation and prognosis, The Journal of Dermatology (2010)
SCL-70 Antibody, UI Health Care (University of Iowa Hospitals & Clinics) Laboratory Services Handbook

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.