From the Guidelines
The diagnosis of Systemic Lupus Erythematosus (SLE) relies on a combination of blood tests, including the antinuclear antibody (ANA) test, anti-double stranded DNA (anti-dsDNA) testing, and other autoimmune markers, which should be interpreted alongside clinical symptoms and physical examination findings. When diagnosing SLE, the initial step involves testing for the presence of ANA, and if positive, further testing for anti-dsDNA is recommended, as suggested by recent guidelines 1. The reference method for anti-dsDNA detection is the Farr assay, but due to its limitations, a double-screening strategy using a last-generation SPA (such as FEIA, CLIA, ELISA, or multiplex assay) followed by the CLIFT as a confirmation test is recommended 1. Key blood tests for SLE diagnosis include:
- Antinuclear antibody (ANA) test
- Anti-double stranded DNA (anti-dsDNA) testing using a double-screening strategy with SPA and CLIFT
- Anti-Smith antibodies
- Complement levels (C3 and C4)
- Complete blood count
- Comprehensive metabolic panel
- Erythrocyte sedimentation rate (ESR)
- C-reactive protein (CRP)
- Anti-phospholipid antibodies (anticardiolipin, anti-β2GP1, and/or lupus anticoagulant) to assess clotting risk, as 30-40% of SLE patients are positive for these antibodies 1. It is essential to interpret these test results in the context of clinical symptoms, as no single test confirms lupus, and diagnosis ultimately requires meeting clinical criteria that combine laboratory findings with physical symptoms like rash, joint pain, and organ involvement 1.
From the Research
Blood Tests for Systemic Lupus Erythematosus (SLE) Diagnosis
The following blood tests are used to diagnose and monitor SLE:
- Complete blood picture (CBC) to evaluate hematological abnormalities such as anemia, leukopenia, and thrombocytopenia 2, 3, 4
- Liver function tests to assess liver involvement 2
- Kidney function tests to evaluate renal involvement 2
- Antinuclear antibody (ANA) test to detect the presence of autoantibodies 2
- Anti-double stranded DNA (anti-dsDNA) antibody test to assess disease activity 2, 5
- Complement system tests, including C3 and C4 levels, to evaluate the immune system's response 2, 3, 5
- Anti-C1q antibody test to detect the presence of autoantibodies associated with lupus nephritis 2
- Thrombopoietin levels and anti-thrombopoietin antibodies to assess thrombocytopenia 6
- Soluble transferrin receptor (sol TFR) levels to evaluate iron deficiency and anemia 4
- Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) levels to assess disease activity 3, 4
Specific Markers for Lupus Nephritis
The following markers are used to assess lupus nephritis:
- Urinary MCP-1 and IP-10 levels to evaluate renal activity 5
- Anti-C1q antibody test to detect the presence of autoantibodies associated with lupus nephritis 2
- Complement system tests, including C3 and C4 levels, to evaluate the immune system's response 2, 3, 5
Hematological Profiles and Complement System
The relationship between hematological profiles and the complement system in SLE patients has been studied, and the results show that:
- Lower values of C1q and C2 are associated with lower hemoglobin levels 3
- Lower leukocyte counts are associated with lower values of C4, C1 inhibitor, C3, factor D, and alternative pathway functional levels 3
- Neutrophil counts are negatively correlated with the alternative pathway and C1-inh 3
- Lymphocyte counts are associated with functional tests of the classical and alternative pathways, as well as with C2, C4, C3, and C3a 3
- Platelet counts are associated with lower C2 concentrations 3