From the Guidelines
Yes, ENA ABS (Extractable Nuclear Antigen Antibodies) testing, specifically for anti-RNP and anti-Smith antibodies, is indicated in systemic lupus erythematosus (SLE). According to the European League Against Rheumatism recommendations for monitoring patients with SLE, laboratory assessment should include the monitoring of autoantibodies such as ANA, anti-dsDNA, anti-Ro, anti-La, anti-RNP, anti-Sm, and anti-phospholipid, as well as complement levels like C3 and C4 1.
Key Points for ENA ABS Testing in SLE
- Anti-Smith antibodies are highly specific for SLE, with a specificity of 95-98%, making them valuable diagnostic markers when present, though their sensitivity is only about 30% 1.
- Anti-RNP antibodies are found in approximately 30-40% of SLE patients and are also associated with mixed connective tissue disease.
- These antibodies help in confirming an SLE diagnosis, particularly in cases with clinical features suggestive of lupus but inconclusive ANA results.
- The presence of anti-Smith antibodies is included in both the American College of Rheumatology and the Systemic Lupus International Collaborating Clinics classification criteria for SLE.
- Testing for these antibodies is typically performed as part of a comprehensive autoantibody panel in patients with suspected SLE, alongside other tests like ANA, anti-dsDNA, and complement levels.
Clinical Utility of ENA ABS Testing
The results of ENA ABS testing can influence treatment decisions and help monitor disease activity in established SLE patients. For instance, changes in anti-double-stranded (ds) DNA antibody titers sometimes correlate with disease activity and active renal disease, and may be useful in monitoring disease activity 1. Similarly, anti-Ro, anti-La, and anti-ribonucleoprotein (RNP) antibodies may have prognostic value in SLE, with anti-Ro/Sjögren syndrome antigen A (SSA) and anti-La (SSB) antibodies associated with the occurrence of neonatal lupus.
Recommendations for Clinical Practice
In clinical practice, ENA ABS testing should be considered as part of the initial diagnostic workup for SLE, particularly in patients with clinical features suggestive of lupus but inconclusive ANA results. Additionally, regular monitoring of autoantibody levels, including anti-RNP and anti-Smith antibodies, may be useful in assessing disease activity and guiding treatment decisions. However, the decision to test for these antibodies should be individualized based on the patient's clinical presentation and risk factors.
From the Research
ENA ABS (Anti RNP & Anti Smith) in SLE
- ENA ABS, including anti-RNP and anti-Smith antibodies, are associated with disease activity and severity in Systemic Lupus Erythematosus (SLE) patients 2, 3.
- The presence of anti-Smith antibodies is correlated with higher SLE disease activity index (SLEDAI) and anti-dsDNA titer 2.
- Anti-RNP autoantibodies are associated with the interferon gene signature but not decreased complement levels in SLE patients 4.
- A combination of anti-Smith, anti-Ro, and anti-ribonucleoprotein antibodies is associated with an accelerated development of lupus nephritis in SLE patients 3.
- Monitoring of anti-Sm antibody titer may help assess disease activity in SLE, and regular monitoring of high-risk patients can reduce the burden of lupus nephritis and its complications 2, 3.
Diagnosis and Risk Stratification
- Anti-RNP autoantibodies can occur in mixed connective tissue disease (MCTD) or SLE, and MCTD criteria are associated with reduced rates of renal disease in SLE patients 5.
- The question of MCTD versus SLE is not either/or, as most MCTD patients also have lupus 5.
- A specific antibody profile, including anti-Sm, anti-Ro, and anti-RNP, can help identify SLE patients at high risk of developing lupus nephritis 3.