From the Guidelines
To diagnose Systemic Lupus Erythematosus (SLE), a combination of laboratory tests is necessary, including the antinuclear antibody (ANA) test, anti-double-stranded DNA (anti-dsDNA) and anti-Smith (anti-Sm) antibodies, as well as a complete blood count (CBC), comprehensive metabolic panel, urinalysis, and complement levels, as recommended by the most recent expert panel proposal 1. The diagnosis of SLE is complex and requires a multi-step approach.
- The ANA test is the first step, as it is positive in almost all lupus patients, although it can also be positive in other conditions 1.
- If the ANA test is positive, more specific antibody tests are usually ordered, including anti-dsDNA and anti-Sm antibodies, which are highly specific for lupus 1.
- Additional antibody tests may include anti-SSA/Ro, anti-SSB/La, and anti-RNP, as they may have prognostic value in SLE 1.
- A CBC is essential to check for anemia, low white blood cell count, or low platelet count, which are common in lupus 1.
- Comprehensive metabolic panel and urinalysis help assess kidney function, as lupus can cause kidney damage 1.
- Complement levels (C3 and C4) are often measured, as low levels can indicate active lupus 1.
- Erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) tests measure inflammation, although the significance of CRP in SLE remains controversial 1. The most recent expert panel proposal recommends a double-screening strategy using a last-generation SPA in the first place and, subsequently, the CLIFT as the confirmation test for anti-dsDNA antibodies 1.
- In the event of a negative SPA result, a confirmatory CLIFT should be done only when other signs of clinical suspicion are present 1.
- The laboratory should include the method used in their reports, and if several methods are used, the results obtained with each method should be reported 1.
From the Research
Laboratory Tests for Diagnosing Systemic Lupus Erythematosus (SLE)
The following laboratory tests are used to diagnose SLE:
- Antinuclear antibody (ANA) test: This test is highly sensitive for SLE, but its specificity is low 2, 3, 4
- Anti-double-stranded DNA (anti-dsDNA) antibodies: These antibodies are highly specific for SLE and can be detected using the Farr assay or immunofluorescence on Crithidia Luciliae 2, 3, 5
- Anti-nucleosome antibodies: These antibodies may be one of the earliest and most sensitive markers for SLE diagnosis, particularly in patients who are anti-dsDNA negative 6, 3
- Complement tests (C3 and C4 levels): These tests can be used to monitor disease activity and correlate with clinical condition 6, 3
- Extractable nuclear antigens (ENA) and phospholipid antibodies: These tests can be used to identify subgroups of patients at risk for certain clinical manifestations 3
- Urinary levels of monocyte chemoattractant protein 1 (MCP1): This test may be useful for monitoring nephritis activity in lupus patients 3
Recommended Laboratory Procedures
The following laboratory procedures are recommended for diagnosing and monitoring SLE:
- Indirect immunofluorescence on Hep-2 cells for ANA detection 3
- Farr assay or immunofluorescence on Crithidia Luciliae for anti-dsDNA detection 2, 3
- Quantitative determination of anti-dsDNA for monitoring patients 3
- Combined detections of autoantibodies (ANA, ENA, anti-dsDNA) to improve sensitivity and efficiency of laboratory diagnosis 5