Figure 1 Suggested diagnostic protocol for investigation of suspected SLE. *Confirm weak positives or possible false positives by IgG CLIF; **confirm weak positives or possible false positives by ID/CIE/IB. Antiphospholipid/lupus anticoagulant assays might be necessary if relevant clinical features of an antiphospholipid syndrome are present. ANA, antinuclear antibody; CIE, countercurrent immunoelectrophoresis; CLIF, Crithidia luciliae immunofluorescence; CRP, C reactive protein; dsDNA, double stranded DNA; ELISA, enzyme linked immunosorbent assay; ENA, extractable nuclear antigen; ESR, erythrocyte sedimentation rate; ID, immunodiffusion; IB, immunoblotting; PCNA, proliferating cell nuclear antigen.