What is S-Anti-RNP(U1)?
S-Anti-RNP(U1) is an autoantibody directed against U1 ribonucleoprotein, a component of the cell nucleus's RNA processing. This antibody is primarily associated with mixed connective tissue disease (MCTD), but can also be found in systemic lupus erythematosus (SLE), systemic sclerosis, and myositis. The antibody is analyzed as part of a blood test when a systemic autoimmune disease is suspected.
Why is S-Anti-RNP(U1) tested?
S-Anti-RNP(U1) is tested to:
- Diagnose suspected mixed connective tissue disease (MCTD)
- Identify overlapping features between different connective tissue diseases (e.g. SLE, scleroderma and polymyositis)
- Provide support for diffuse symptoms such as fatigue, muscle pain, joint pain and Raynaud's phenomenon
- Differentiate MCTD from similar autoimmune conditions
How do you interpret test results from S-Anti-RNP(U1)?
A positive S-Anti-RNP(U1) is strongly associated with MCTD, especially when no other autoantibodies predominate. It also occurs in milder forms in SLE or other autoimmune diseases. High levels in combination with typical symptoms suggest MCTD, while lower levels may be seen as part of an overlapping syndrome.
Unlike some other autoantibodies, S-Anti-RNP is not used to monitor disease activity over time, but as a diagnostic marker. A positive result should always be interpreted together with clinical findings and other laboratory tests, such as ANA and ENA panel.