From the Guidelines
The best test for Systemic Lupus Erythematosus (SLE) is the anti-nuclear antibodies (ANA) test, specifically the indirect immunofluorescence assay (IIFA) on HEp-2 cells, as it is considered the first level test for laboratory diagnosis of SLE.
Key Points
- The ANA test is the initial screening test for SLE, with a recommended screening dilution of 1:160 on conventional HEp-2 substrates 1.
- If the ANA test is positive, testing for anti-dsDNA antibodies is advised when there is clinical suspicion of SLE, using methods such as the Farr assay or the Crithidia luciliae immunofluorescence test (CLIFT) 1.
- The CLIFT is considered pathognomonic for SLE, but has low sensitivity, while solid-phase assays (SPAs) such as ELISA or FEIA are less specific but have varying sensitivity 1.
- A double-screening strategy using a last-generation SPA followed by CLIFT as a confirmation test is recommended for anti-dsDNA testing 1.
- The method used for anti-dsDNA antibody detection should be included in the test result, and results should be reported quantitatively or semiquantitatively 1.
Testing Strategy
- If ANA is positive, proceed with anti-dsDNA testing using a SPA, followed by CLIFT if the SPA is positive 1.
- If ANA is negative, do not investigate anti-dsDNA unless there is a high degree of clinical suspicion 1.
- If the CLIFT assay is positive but the SPA is negative, the result should be explained, and the laboratory may recommend repeating the anti-dsDNA assays in a new sample 1.
From the Research
Diagnostic Tests for Systemic Lupus Erythematosus (SLE)
The diagnosis of SLE involves a combination of clinical and laboratory criteria. The following are some of the key tests used in the diagnosis of SLE:
- Antinuclear antibody (ANA) test: This is the most sensitive test for SLE and is used as a screening test 2, 3, 4, 5, 6
- Anti-dsDNA antibodies: These are highly specific for SLE and are present in a high proportion of SLE patients 2, 3, 4
- Anti-Sm (Smith antigen) test: This is also highly specific for SLE and has strong confirmatory powers 3, 4
- Antibodies to extractable nuclear antigens (ENA) and phospholipids: These are useful in identifying subgroups of patients at risk for certain clinical manifestations 2
- Urinary levels of monocyte chemoattractant protein 1 (MCP1): These are useful in monitoring nephritis activity in lupus patients 2
Interpretation of Test Results
The results of these tests must be interpreted in the context of the patient's clinical symptoms and history. A positive ANA test is not specific for SLE and can be present in other conditions, so additional testing and clinical evaluation are necessary to confirm the diagnosis 2, 3, 4, 5, 6. The American College of Rheumatology recommends that the ANA test be obtained only in patients with unexplained involvement of two or more organ systems 4.
Testing Approach
A combination sequential testing approach may be a logical approach to diagnosing SLE, starting with the ANA test and followed by more specific tests such as anti-dsDNA and anti-Sm antibodies if the ANA test is positive 3, 4. New assays such as anti-C1q and anti-nucleosome antibodies have been proposed for diagnosis and monitoring of SLE patients, but more research is needed to fully evaluate their usefulness 2.