Scl-70 (anti-topoisomerase) Ab in serum
Indications
- evaluation of scleroderma
- diffuse scleroderma (20-50%)
Reference interval
- Normal: Negative
Principle
Scl-70 antigen is purified from calf thymus, bound to microwells and stabilized for extended shelf life. Diluted patient sera are placed in the microwells & incubated. If anti-Scl-70 antibodies are present, they will bind to the antigen in the microwell. After washing the microwells to remove residual sample, a second incubation with anti-human IgG conjugated to alkaline phosphatase is carried out. Conjugate will bind immunologically to the anti- scl-70 IgG of the antigen-antibody complex, forming a 'sandwich' consisting of:
Conjugate (Enzyme-labeled Anti-human IgG)
Human anti-Scl-70 (IgG)
Well Coated with Scl-70 antigen
Unbound conjugate is removed in the subsequent washing step. Enzyme substrate is then added to the microwell & if bound conjugate is present, the colorless substrate (p-nitrophenyl phosphate) will be hydrolyzed to form a yellow end product (p-nitrophenol). The intensity of the color is measured photometrically at 405 nm & is proportional to the concentration of anti-Scl-70 present in the patients sample.
Clinical significance
- 2 autoantibodies have been identified which are present almost exclusively in scleroderma
- anti-Scl-70 antibody is found in 20-50% of patients with diffuse scleroderma
- anti-Scl-70 Ab is directed against a 70kDa nuclear protein identified as topoisomerase 1
- more likely in scleroderma patients with pulmonary fibrosis[5]
- anti-centromere antibody is strongly associated with limited scleroderma, or CREST syndrome
- anti-centromere Ab is directed against the chromosomal kinetochore
- anti-Scl-70 antibody is found in 20-50% of patients with diffuse scleroderma
- detection of either of these 2 autoantibodies is highly is highly specific for scleroderma
- because these 2 autoantibodies rarely occur in the same patient, they are useful in determining the scleroderma subtype, diffuse or limited (CREST syndrome)
Specimen
Serum is separated from the clot & refrigerated, 2-8 degrees C for short term storage or stored frozen, -20 degrees C, for long term storage. Avoid freeze-thaw cycles. CAUTION: Serum samples should not be heat inactivated, as this may cause false positive results.
No special patient preparation required.
Interpretation
- <20 EU/mL: negative for antibodies to Scl-70
- 20-25 EU/mL: Equivocal for antibodies to Scl-70
- >25 EU/mL: positive for antibodies to Scl-70
More general terms
More specific terms
Additional terms
Component of
References
- ↑ Henry, John Bernard, Clinical Diagnosis amd Management by Laboratory Methods, W. B. Saunders Co., Philadelphia, 1991. pp 891-892.
- ↑ The Physicians Guide to ENA Testing, Diamedix Corporation, Miami, 1991. pp 1-8.
- ↑ Summary of Procedure. DiaMedix Corporation, Miami, Oct. 1991. pp 1-8.
- ↑ Poly-ENA Extractable Nuclear Antigen Assay for Detection of Antibodies to RNP, Sm, and/or SSA (RO), & SSB (LA). Zeus Scientific, Inc., Raritan, New Jersey, 1987. pp 1-5.
- ↑ 5.0 5.1 Medical Knowledge Self Assessment Program (MKSAP) 14, 17. American College of Physicians, Philadelphia 2006, 2015