Testing for the level of complement C4d on erythrocytes and on B cells, alongside ELISAs for anti-dsDNA antibodies and antinuclear antibodies, provides an index score with 80% sensitivity for systemic lupus erythematosus (SLE). In a multicentre study that enrolled 210 patients with SLE, 178 people with other rheumatic diseases and 205 healthy controls, the specificity for SLE of this score was 87%.