From the Guidelines
Diagnosing Systemic Lupus Erythematosus (SLE) requires a combination of laboratory tests, with antinuclear antibody (ANA) testing being the most important, followed by more specific antibody tests such as anti-double-stranded DNA (anti-dsDNA) and anti-Smith (anti-Sm) antibodies, as recommended by recent guidelines 1. The diagnostic laboratory tests for SLE include:
- Antinuclear antibody (ANA) testing, which is positive in over 95% of lupus patients, though it can be positive in other conditions as well
- Anti-double-stranded DNA (anti-dsDNA) antibody testing, which is highly specific for lupus and recommended for all ANA-positive cases with clinical suspicion of SLE 1
- Anti-Smith (anti-Sm) antibodies, which are highly specific for lupus
- Complete blood count (CBC) to check for anemia, leukopenia, or thrombocytopenia
- Comprehensive metabolic panel to assess kidney and liver function
- Urinalysis to detect protein or blood in urine indicating kidney involvement
- Complement levels (C3 and C4), which are often low in active lupus
- Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) to measure inflammation
- Antiphospholipid antibodies if blood clotting issues are suspected These tests should be interpreted alongside clinical symptoms and physical examination findings, as lupus presents differently in each patient. Regular monitoring of these lab values is essential for tracking disease activity and adjusting treatment plans, particularly for patients with organ involvement such as lupus nephritis, as recommended by the EULAR guidelines 1. It is also important to note that the presence of anti-ENA autoantibodies, such as anti-chromatin, anti-ribosomal P protein, and anti-Sjögren syndrome type A and B antigens, can be useful in the diagnosis and follow-up of SLE, as suggested by recent studies 1. In cases where the results of different tests are contradictory, international detection methods and discrepancy resolution recommendations should be followed, as recommended by expert panels 1.
From the Research
Diagnostic Laboratory Tests for Systemic Lupus Erythematosus (SLE)
The diagnosis of SLE involves various laboratory tests, including:
- Indirect immunofluorescence on Hep-2 cells for the detection of anti-nuclear antibodies (ANA) 2
- Detection of anti-dsDNA antibodies using the Farr assay or immunofluorescence on Crithidia Luciliae 2
- Quantitative determination of anti-dsDNA for monitoring patients, particularly in the presence of nephritis 2
- Detection of antibodies to extractable nuclear antigens (ENA) and to phospholipids (Lupus anticoagulant and anti-cardiolipin antibodies) 2
- New assays such as anti-C1q and anti-nucleosome antibodies for diagnosis and monitoring SLE patients 2
- Urinary levels of monocyte chemoattractant protein 1 (MCP1) to monitor nephritis activity in lupus patients 2
- Complement levels in blood and complement deposition in histological tests for the management of SLE 3
- Novel complement biomarkers such as split products and cell-bound complement activation products for more sensitive detection 3
- Anti-Sm antibodies for diagnosis, especially in anti-dsDNA-negative patients 4
Specificity and Sensitivity of Diagnostic Tests
- ANA test has high sensitivity (almost 100%) but low specificity since ANA can be present in other clinical conditions and normal controls 2, 5
- Anti-dsDNA antibodies are highly specific for SLE and present in a high proportion of SLE patients (40-80%) 2
- Anti-Sm antibodies have a sensitivity of 25.9% and specificity of 99% 4
- Anti-dsDNA antibodies have a sensitivity of 30.2% and specificity of 99% 4
Clinical Significance of Diagnostic Tests
- Anti-Sm antibodies are associated with age, number of ACR criteria, renal and neurologic disorder, and cross-sectional disease activity 4
- Anti-Sm antibodies are essential for diagnosis of SLE, especially in anti-dsDNA-negative patients 4
- Monitoring of anti-Sm antibodies is only helpful in SLE patients with active lupus nephritis 4