From the Guidelines
Being ANA positive and ENA negative indicates the presence of autoantibodies targeting the nucleus, but not the specific extractable nuclear antigens tested in the ENA panel, which may suggest early or mild autoimmune disease, drug-induced autoimmunity, or a false-positive ANA result. This pattern is relatively common and its clinical significance depends on the patient's symptoms, ANA titer and pattern, and other laboratory findings 1. ANA is a broader screening test that detects antibodies against various nuclear components, while ENA testing looks for specific antibodies like anti-Ro/SSA, anti-La/SSB, anti-Sm, and anti-RNP.
Some key points to consider in this scenario include:
- The use of a 1:160 dilution as the cut-off point for ANA detection, which increases the positive likelihood ratio and diagnostic performance in unselected populations 1
- The importance of accompanying analytical requests with pertinent clinical information to help laboratories assess results and decide on subsequent studies 1
- The recommendation to test for anti-ENA antibodies, specifically anti-Ro autoantibodies, in cases with ANA titers between 1:80 and 1:160 to further elucidate the diagnosis 1
- The need for laboratories to specify the methods used for detecting ANA and to report results according to standardized terminology 1
While this pattern doesn't rule out autoimmune disease, it's generally associated with a lower likelihood of specific conditions like lupus or Sjögren's syndrome compared to when both tests are positive. Follow-up testing and clinical monitoring are typically recommended for patients with this pattern, especially if symptoms suggest autoimmune disease. It is essential to interpret ANA results in the context of clinical manifestations and to exercise caution when using the 1:80 cut-off point due to its low positive likelihood ratio 1.
From the Research
Definition of ANA and ENA
- Anti-Nuclear Antibody (ANA) is an immunoglobulin directed against autologous cell nuclear and cytoplasmic components 2
- Extractable Nuclear Antigen (ENA) is a type of antigen that can be extracted from cell nuclei and is recognized by ANA 3
Being ANA Positive and ENA Negative
- A positive ANA test indicates the presence of autoantibodies against nuclear and cytoplasmic components, but it does not specify the type of antigen being targeted 2
- An ENA negative result means that the autoantibodies present do not react with extractable nuclear antigens, which can help differentiate between distinct types of autoimmune connective tissue diseases 3
- The absence of ENA antibodies does not rule out the presence of autoimmune disease, as some diseases may not involve ENA antibodies 4
Clinical Implications
- A positive ANA test should be followed by an anti-ENA antibody assay to further characterize the autoantibodies and aid in diagnosis 3
- The pattern and titer of ANA, as well as the presence or absence of ENA antibodies, should be taken into account when evaluating a patient's condition 2
- The detection of ENA antibodies can be useful in diagnosing and managing autoimmune diseases, but it is essential to consider the clinical presentation and other laboratory results in conjunction with ENA antibody testing 5