What is the best testing to diagnose Systemic Lupus Erythematosus (SLE)?

Best Testing to Diagnose Systemic Lupus Erythematosus

Begin with ANA testing by indirect immunofluorescence on HEp-2 cells at a titer ≥1:80 as the mandatory entry criterion, followed by a double-screening strategy for anti-dsDNA antibodies using a solid-phase assay (FEIA, CLIA, or ELISA) confirmed by Crithidia luciliae immunofluorescence test (CLIFT), along with anti-Sm and anti-ENA panel testing when ANA is positive. 1, 2

Initial Screening: ANA Testing

• ANA by indirect immunofluorescence on HEp-2 cells is the required entry criterion for SLE classification per EULAR/ACR 2019 criteria, with a positive result defined as titer ≥1:80 1
• ANA has nearly 100% sensitivity for SLE, making it the best screening test to rule out the disease 3, 4, 5
• Only perform ANA testing when clinical suspicion exists: unexplained rashes, arthritis, serositis, neurological manifestations, or cytopenias 2, 5
• Testing in low-prevalence populations without clinical features leads to false positives and should be avoided 2, 5

Critical caveat: ANA has low specificity—it can be positive in many other conditions and even healthy individuals 3, 4. Never diagnose SLE based on ANA alone.

Confirmatory Testing: Anti-dsDNA Antibodies

Use a sequential double-screening strategy for anti-dsDNA testing 1, 2:

1. First step: Solid-phase assay (SPA) such as FEIA, CLIA, or ELISA—these are highly sensitive but less specific 1, 2
2. Second step: Crithidia luciliae immunofluorescence test (CLIFT) for confirmation—this is pathognomonic with very high specificity but low sensitivity 1, 2

Interpretation of Anti-dsDNA Results:

• SPA positive + CLIFT positive: SLE very likely—proceed with diagnosis in appropriate clinical context 1
• SPA positive + CLIFT negative: Evaluate carefully with clinical characteristics; may represent false positive 1
• SPA negative + CLIFT negative: SLE diagnosis cannot be established at this time 1
• SPA negative + CLIFT positive: Inconsistent result—repeat testing in new sample and maintain clinical follow-up 1

Important note: Anti-dsDNA antibodies are highly specific for SLE (present in 40-80% of patients) and have strong confirmatory power 3, 4, 6

Additional Confirmatory Antibody Testing

When ANA is positive, obtain an anti-ENA panel including 2, 7:

• Anti-Sm antibodies: Highly specific for SLE with strong confirmatory value 2, 3, 5
• Anti-Ro/SSA and anti-La/SSB: Provide prognostic information for specific manifestations 2
• Anti-RNP: Part of comprehensive evaluation 2

Testing note: Anti-nucleosome antibodies show excellent performance with 90% sensitivity and 88% specificity, particularly useful in lupus nephritis 6

Essential Routine Laboratory Tests

Complete the diagnostic workup with 2, 7:

• Complement levels (C3 and C4): Low levels correlate with disease activity and major organ involvement 2, 7
• Complete blood count (CBC): Detect cytopenias (anemia, leukopenia, lymphopenia, thrombocytopenia) that correlate with disease activity 2, 7
• Renal function assessment: Serum creatinine, urinalysis with microscopy, and quantification of proteinuria for prognostic information 2, 7
• Antiphospholipid antibodies: Lupus anticoagulant and anti-cardiolipin antibodies to identify patients at risk for thrombosis 7, 4

Testing Algorithm Summary

For patients with clinical suspicion of SLE 1, 2:

1. Order ANA by indirect immunofluorescence on HEp-2 cells
2. If ANA ≥1:80: Proceed with anti-dsDNA double screening (SPA then CLIFT), anti-ENA panel, complement levels, CBC, renal function tests, and antiphospholipid antibodies
3. If ANA negative but high clinical suspicion persists: Consider anti-dsDNA testing and maintain clinical follow-up, as antibodies may appear before clinical manifestations 1, 2
4. If ANA negative with low clinical suspicion: SLE effectively ruled out 3, 5

Common pitfall: Avoid ordering ANA reflexively without clinical suspicion—the low positive predictive value in low-prevalence populations generates unnecessary follow-up testing and patient anxiety 2, 5, 8. The test should only be ordered when multisystem inflammatory features suggest SLE.