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Table 1 Sensitivity and specificity as diagnostic indicators for rheumatoid arthritis for antibodies against cyclic citrullinated peptide (anti-CCP Ab) and for rheumatoid factor (RF) of IgA, IgM, and IgG isotypes, in combination with the presence of a shared epitope (SE) allele – HLA-DRB1*0401 or B1*0404 – in 59 'prepatients' whose blood samples antedated the appearance of symptoms of rheumatoid arthritis (median 2.0 years [interquartile range 0.9–3.9]) and in 118 matched controls.

From: A combination of autoantibodies to cyclic citrullinated peptide (CCP) and HLA-DRB1 locus antigens is strongly associated with future onset of rheumatoid arthritis

Variables Sensitivity Specificity
  % 95%CI % 95%CI
Anti-CCP Ab 37 25–51 98 93–100
IgA-RF 42 29–56 94 87–98
IgM-RF 22 12–35 94 87–98
IgG-RF 17 8–30 94 87–98
SE (B1*0404 or 0401)1 60 45–72 64 54–73
SE + anti-CCP Ab 28 17–42 99 94–100
SE + IgA-RF 25 14–38 98 93–100
SE + IgM-RF 14 6–27 98 93–100
SE + IgG-RF 11 4–22 99 94–100
SESE (B1*0404 or 0401)1 28 17–42 95 88–98
SESE + anti-CCP Ab 14 6–27 99 94–100
SESE + IgA-RF 7 2–18 99 94–100
SESE + IgM-RF 5 1–16 99 94–100
SESE + IgG-RF 4 0–14 100 95–100
  1. 1Analysed in 57 prepatients and in 112 controls. CI, confidence interval.