Table 2

Stepwise addition of CBCAPS and antibody components to ANA, anti-dsDNA and anti-Sm serologies

Model #1Model #2: model #1+specificity componentModel #3: model #1+CBCAPSModel #4: model #1+CBCAPS+specificity component
Tier1dsDNA; SmdsDNA; SmdsDNA; Sm; EC4d; BC4ddsDNA; Sm; EC4d; BC4d
Tier 2ANA*ANA*+Antibody specificity†ANA*+CBCAPS‡ANA*+CBCAPS‡+Antibody specificity†
Total sensitivity (%)89838480
Total specificity (others) (%)53767086
Sjogren's syndrome (%)12615270
Scleroderma (%)34775791
PM/DM  (%)26415974
RA (%)67867792
Other diseases (%)69697676
Specificity (NHV) (%)90919598
Two-tiered AUC 0.7810.8040.8940.913§
  • The diagnostic methodology involved two consecutive ‘tiers’ of analysis in which the aggregated diagnostic value of anti-dsDNA, anti-Sm, ANA combined with CBCAPS (EC4d and BC4d) and antibody specificity component (positivity to either anti-MCV, SS-B/La, Jo-1, Scl-70 or CENP) (model #4 as presented figure 1) was compared with model #1.

  • Model#1 relied on anti-dsDNA (>301 units confirmed by Crithidia) or anti-Sm (>10 units) reactivities in tier 1. Tier 2 was determined among subjects negative in tier 1 and consisted of an index score of the ANA component only (as defined in figure 1 legend); positivity for the index score (>0) was indicative of SLE, and the two-tier combination resulted in the overall performance characteristics (total sensitivity and total specificity). The stepwise addition of CBCAPS (model #3) and the antibody specificity component (model #4) to model #1 maximised the performances characteristics.

  • Total sensitivity and specificity are SLE vs. all others diseases. The individual sensitivities and specificities are SLE vs. the individual disease.

  • *ANA component.

  • †Antibody specificity component.

  • ‡CBCAPS component.

  • §p<0.01 vs. model 1, 2 and 3.

  • ANA, antinuclear antibodies; anti-Sm, anti-Smith; AUC, area under the curve; CBCAPS, complement C4 activation products; anti-dsDNA, antibodies to double-stranded DNA; PM/DM, polymyositis/dermatomyositis; RA, rheumatoid arthritis; SLE, systemic lupus erythematosus; NHV, normal healthy volunteers; anti-MCV, anti-mutated citrullinated vimentin; EC4d, complement C4d levels on erythrocytes;  BC4d, complement C4d levels on cells; CENP, Centromere extractable nuclear antigen; Scl, scleroderma; SS, Sjogren's syndrome.