SSA/Ro Ab in serum
Etiology
- Sjogren's Syndrome (60-70%)
- systemic lupus erythematosus (SLE) (30-40%)
- rheumatoid arthritis (RA) (0-5%)
- scleroderma
Reference interval
- Normal: Negative
Principle
Highly purified SSA antigen is bound to microwells & stabilized for extended shelf life. Diluted patient sera are placed in the microwells & incubated. If anti-SSA antibodies are present, they will bind to the antigen in the microwell. The microwells are then washed to remove residual sample & a second incubation with anti-human IgG conjugated to alkaline phosphatase is carried out. The conjugate will bind immunologically to the anti-SSA IgG antigen-antibody complex, forming a 'sandwich' consisting of:
Conjugate (Enzyme-labeled Anti-human IgG)
Well Coated with SSA 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 reaction is then stopped & the color fixed. The intensity of the color is measured photometrically at 405 nm & is proportional to the concentration of anti-SSA present in the patients sample.
Clinical significance
- associated with Sicca symptoms[4]
- associated with photosensitivity
- associated with neonatal lupus[4]
The presence of antibody to the SSA antigen strongly correlates with distinguishable subsets of SLE & Sjogren's Syndrome. Antibody to SSA (Ro) occurs in 62% of patients with 'ANA negative' SLE, 63% to > 85% of patients with subacute cutaneous lupus erythematosus, 75% of the homozygous C2-deficient patients with SLE-like picture, & in 80% of patients with Sjogren's Syndrome who have vasculitis. The existence of the autoantibody in pregnant mothers has been closely associated with the development of neonatal congenital heart block and neonatal lupus: thus the screening of pregnant SLE patients for anti-SSA antibodies is recommended.
SLE patients who have anti-SSA antibodies alone can be distinguised clinically & serologically from those who produce both anti-SSA & SSB antibodies. For example, nephritis occurs much more frequently in the former group than the latter. In addition, the incidence & levels of anti-DNA antibodies are significantly greater in patients with SSA antibodies alone compared to those with SSA & SSB antibodies. Patients producing anti-SSA alone never have been observed to produce anti-SSB whereas those producing both antibodies have not thus far been observed to cease having one or the other antibody in their sera. Fluctuating titers of anti-SSA antibodies in some SLE patients have been reported. In this case the changes in anti-SSA levels often correlated with disease activity & anti-DNA antibody levels.
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 SSA
- 20-25 EU/mL: Equivocal for antibodies to SSA
- >25 EU/mL: Positive for antibodies to SSA
More general terms
More specific terms
- Sjogrens syndrome-A extractable nuclear IgG Ab in serum; anti-SSA IgG in serum
- SSA/Ro 52KB Ab in serum
- SSA/Ro 60KB Ab in serum
Additional terms
- 52 kD Ro protein; Sjoegren syndrome type A antigen; SS-A; Ro(SS-A); 52 kD ribonucleoprotein autoantigen Ro/SS-A; tripartite motif-containing protein 21; RING finger protein 81 (TRIM21, RNF81, Ro52, SSA1)
- 60 kD SS-A/Ro ribonucleoprotein; 60 kD ribonucleoprotein Ro; RoRNP; 60 kD Ro protein; Ro 60 kD autoantigen; TROVE domain family member 2; Sjoegren syndrome type A antigen; SS-A; Sjoegren syndrome antigen A2 (TROVE2, Ro60, SSA2)
- anti-SSA/Ro
- SSB/La Ab in serum
Component of
References
- ↑ Henry, John Bernard, Clinical Diagnosis amd Management by Labortory Methods, W. B. Saunders Co., Philadelphia, 1991. pp 891-892.
- ↑ The Physicians Guide to Anti-DNA Antibody Testing, Diamedix Corporation, Miami, Aug. 1989. pp 1-6.
- ↑ Summary of Procedure. DiaMedix Corporation, Miami, June 1991. pp 1-8
- ↑ 4.0 4.1 4.2 4.3 Medical Knowledge Self Assessment Program (MKSAP) 11, 17, 19. American College of Physicians, Philadelphia 1998, 2015, 2022