From the Guidelines
A positive ANA test result for Systemic Lupus Erythematosus (SLE) diagnosis is typically considered at a titer of 1:80 or higher, as recommended by the EULAR/ACR 2019 classification criteria 1. However, it is essential to note that a positive ANA alone is not sufficient to diagnose lupus, as approximately 15-25% of healthy individuals can have a positive ANA test. The pattern of fluorescence (homogeneous, speckled, nucleolar, etc.) is also important in interpretation. For a lupus diagnosis, doctors typically look for a positive ANA along with clinical symptoms and other laboratory findings. The higher the titer, the more likely it is to be clinically significant, with values of 1:640 or higher strongly suggesting an autoimmune condition like lupus. If you have a positive ANA test, further specific antibody tests such as anti-dsDNA and anti-Smith antibodies are usually needed to confirm a lupus diagnosis.
Some key points to consider when interpreting ANA test results include:
- The EULAR/ACR 2019 classification criteria recommend ANA detection using the indirect immunofluorescence test on HEp-2 cells (IFI) or a solid-phase ANA screening immunoassay (SPA) with at least equivalent performance 1.
- The use of a 1:80 cut-off point for ANA positivity has a relatively low specificity of 74.7% (IC 95%: 66.7% - 81.3%) 1.
- Increasing the cut-off point to 1:160 can improve specificity to 86.2% (IC 95%: 80,4% - 90,5%) while maintaining an appropriate sensitivity (95,8%; IC 95%: 94,1% - 97,1%) 1.
- Cases with ANA titers between 1:80 and 1:160 may be further elucidated by testing anti-ENA, specifically anti-Ro autoantibodies 1.
In clinical practice, it is crucial to exercise caution when interpreting ANA test results, especially in populations with low SLE prevalence, and to consider the clinical context and other laboratory findings to confirm a lupus diagnosis. The laboratory report should always detail which method was used, and when several methods are used, it is recommended to report the results obtained with each method 1. Ultimately, a comprehensive approach that combines clinical evaluation, laboratory testing, and careful interpretation of results is necessary to accurately diagnose and manage SLE.
From the Research
Threshold for Positive ANA Test Result
The threshold for a positive Antinuclear Antibody (ANA) test result in Systemic Lupus Erythematosus (SLE) diagnosis is a topic of discussion among researchers.
- A study published in 2009 2 suggests that ANA tests showing a speckled pattern should be at a 1:160 titer or higher to be considered positive.
- Another study from 2007 3 found that the best discrimination between healthy individuals and SLE patients was found at a screening dilution of 1:80 and fluorescent intensity of ≥2.
- A 2013 study 4 reported that no antinuclear antibody-associated rheumatic disease was identified in patients with an ANA <1:160.
- More recent studies, such as one from 2023 5, have focused on the clinical diagnoses associated with a positive ANA test in patients with and without autoimmune disease, but do not specifically address the threshold for a positive ANA test result in SLE diagnosis.
- A 2017 review article 6 discusses the complexities of ANA testing, including the fact that up to 20-30% of the healthy population may test positive for ANA, but does not provide a specific threshold for a positive test result.
Key Findings
- The threshold for a positive ANA test result may vary depending on the study and the specific criteria used.
- A screening dilution of 1:80 and fluorescent intensity of ≥2 may be useful in distinguishing between healthy individuals and SLE patients 3.
- ANA titers <1:160 may not be associated with antinuclear antibody-associated rheumatic disease 4.