From the Guidelines
The initial workup for a patient suspected of having Systemic Lupus Erythematosus (SLE) should include a comprehensive clinical evaluation, laboratory tests, and possibly imaging studies, with a focus on assessing disease activity, organ damage, and comorbidities, as recommended by the European League Against Rheumatism (EULAR) 1. The workup should start with a complete blood count (CBC) with differential, comprehensive metabolic panel, urinalysis, and inflammatory markers like erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP).
- Specific autoantibody testing is crucial, including antinuclear antibody (ANA) as the initial screening test, followed by more specific antibodies if ANA is positive:
- anti-double-stranded DNA (anti-dsDNA)
- anti-Smith (anti-Sm)
- anti-SSA/Ro
- anti-SSB/La
- anti-ribonucleoprotein (anti-RNP)
- Complement levels (C3 and C4) should be measured as they are often decreased in active SLE, as noted in recent recommendations for the use of anti-dsDNA autoantibodies in the diagnosis and follow-up of SLE 1. A chest X-ray and electrocardiogram may be appropriate to assess for cardiopulmonary involvement.
- Depending on symptoms, additional tests might include:
- anti-phospholipid antibodies (anticardiolipin, lupus anticoagulant, and anti-β2 glycoprotein I) if thrombotic events are suspected
- a skin or kidney biopsy if organ involvement is suspected
- Vaccination status should also be assessed, with a focus on pneumococcal vaccination, as SLE patients are at higher risk of infections, particularly bacterial infections, as highlighted in a recent systematic review and meta-analysis 1. This comprehensive approach helps establish the diagnosis based on the presence of clinical and immunological criteria, as SLE is a complex autoimmune disease with varied presentations affecting multiple organ systems.
From the Research
Initial Workup for Systemic Lupus Erythematosus (SLE)
The initial workup for a patient suspected of having Systemic Lupus Erythematosus (SLE) involves several laboratory tests and clinical evaluations. Some key components of this workup include:
- Complete Blood Count (CBC) to evaluate for anemia, leukopenia, or thrombocytopenia
- Erythrocyte Sedimentation Rate (ESR) and C-reactive protein (CRP) to assess inflammation, although their utility in distinguishing between SLE flare and infection is limited 2, 3, 4, 5
- Urinalysis to check for proteinuria or hematuria, indicative of renal involvement
- Blood chemistry tests, including liver and kidney function tests
- Antinuclear antibody (ANA) test, which is sensitive but not specific for SLE
- Specific autoantibody tests, such as anti-dsDNA and anti-Sm antibodies, which are more specific for SLE
Distinguishing Between SLE Flare and Infection
Distinguishing between an SLE flare and an infection can be challenging, as both conditions can present with similar symptoms, such as fever and increased inflammatory markers. However, some studies suggest that:
- The ratio of ESR to CRP may be useful in distinguishing between SLE flare and infection, with a higher ratio indicating a flare 4
- CRP levels may be higher in infection than in SLE flare, although this is not always a reliable distinction 2, 3, 5
- Procalcitonin (PCT) may also be useful in diagnosing infections in patients with SLE, although its utility is limited by heterogeneity and risk of bias in existing studies 6
Laboratory Tests
Some key laboratory tests used in the workup for SLE include:
- ESR, which can be elevated in SLE but is not specific for the disease
- CRP, which can be elevated in infection but may not always be elevated in SLE flare
- ANA test, which is sensitive but not specific for SLE
- Specific autoantibody tests, such as anti-dsDNA and anti-Sm antibodies, which are more specific for SLE
- Complement levels, such as C3 and C4, which can be decreased in SLE due to consumption of complement components in the immune complex formation process.