From the Guidelines
Yes, Extractable Nuclear Antigens (ENA) antibodies, specifically Anti-Ribonucleoprotein (Anti-RNP) and Anti-Smith (Anti-Sm) antibodies, are indicated in Systemic Lupus Erythematosus (SLE).
Key Points
- According to the international recommendations for the assessment of autoantibodies to cellular antigens referred to as anti-nuclear antibodies 1, the detection of ANA is the first level test for laboratory diagnosis of SARD, and anti-ENA antibodies testing should be included in the autoantibodies detection as part of the diagnostic work-up of SARD.
- The study recommends that in case of a positive ANA test during the diagnostic work-up, it is recommended to perform specific tests for anti-ENA antibodies, including Anti-RNP and Anti-Sm antibodies 1.
- Another study also recommends confirmatory testing of anti-extractable nuclear antigens autoantibodies (anti-ENA) when ANAs turn out positive during diagnosis 2.
- The most common targets of the autoantibodies detected in SLE include chromatin, ribosomal P protein, spliceosome small nuclear ribonucleoproteins (Smith), and U1-ribonucleoprotein, which supports the use of Anti-RNP and Anti-Sm antibodies in SLE diagnosis 2.
Testing Recommendations
- The method used for anti-ENA antibody detection should be reported, and in case of discrepancy with IIFA or with clinical suspicion, the use of an additional method should be considered 1.
- Results of assays for antibodies to specific ENA should be reported separately, including negative results 1.
- Quantitative determination of positive anti-RNP antibodies is recommended in case of a clinical suspicion of mixed connective tissue disease 1.
From the Research
Extractable Nuclear Antigens (ENA) Antibodies in Systemic Lupus Erythematosus (SLE)
- ENA antibodies, including Anti-Ribonucleoprotein (Anti-RNP) and Anti-Smith (Anti-Sm) antibodies, are associated with SLE 3, 4, 5, 6, 7
- Studies have shown that patients with SLE often have a high frequency of anti-RNP antibodies, which can be used as a marker for the disease 3, 4, 6
- The presence of anti-Sm antibodies is often accompanied by anti-RNP antibodies, suggesting a relationship between the two 4
- Patients with anti-RNP antibodies tend to have a lower incidence of renal disease and a higher incidence of Raynaud's phenomenon, swollen hands, and hypergammaglobulinemia 3, 5
- The combination of anti-ENA antibodies, anti-cardiolipin antibodies, and anti-β2-glycoprotein 1 antibodies has been shown to have high diagnostic value for SLE 7
Clinical Characteristics of Patients with Anti-RNP and Anti-Sm Antibodies
- Patients with anti-RNP antibodies often have overlapping features of SLE, progressive systemic sclerosis, and polymyositis, and tend to have a low incidence of nephritis 3, 5
- Patients with anti-Sm antibodies tend to have a more typical SLE presentation, with a higher incidence of Raynaud's phenomenon 5
- The presence of anti-RNP and anti-Sm antibodies can be used to distinguish a subset of patients with SLE who have a distinct clinical and laboratory profile 3
Diagnostic Value of Anti-ENA Antibodies
- Anti-ENA antibodies, including anti-RNP and anti-Sm antibodies, can be used as biomarkers for the diagnosis of SLE 6, 7
- The combination of anti-ENA antibodies, anti-cardiolipin antibodies, and anti-β2-glycoprotein 1 antibodies has been shown to have high diagnostic value for SLE, with a sensitivity of 82.12% and a specificity of 80.03% 7