Diagnostic accuracy† and OR of RA-related antibodies in prediagnosis serum samples for future RA. Positivity for RF defined on clinical recommendations as present in < 5% of 491 healthy blood donors: RF > 24.4 units/ml; RF-IgM > 13.6 units/ml; RF-IgG > 10.9 units/ml; and RF-IgA > 10.5 units/ml. Positivity for anti-CCP2 based on manufacturer specifications at > 5 units/ml. Positivity for anti-CarP defined as ≥ 2 SD above the mean in healthy controls reserved to define cutoff: anti-CarP-FCS > 427.4 units/ml and anti-CarP-Fib > 233.9 units/ml.
| Antibody | RA, +/76 | Control, +/41 | SN, % | SP, % | OR | 95% CI | p |
|---|---|---|---|---|---|---|---|
| Anti-CCP2 | 34/76 | 0/41 | 44.7 | 100.0 | NA | NA | NA |
| RF | 27/76 | 1/41 | 35.5 | 97.6 | 22.04 | 2.87–169.36 | < 0.01 |
| RF IgM | 32/76 | 5/41 | 42.1 | 87.8 | 5.24 | 1.85–14.82 | < 0.01 |
| RF IgG | 11/76 | 3/41 | 14.5 | 92.7 | 2.14 | 0.56–8.17 | 0.26 |
| RF IgA | 30/76 | 3/41 | 39.5 | 92.7 | 8.26 | 2.34–29.19 | < 0.01 |
| ≥ 1 RF* | 43/76 | 9/41 | 56.6 | 78.1 | 4.63 | 1.95–11.03 | < 0.01 |
| ≥ 2 RF* | 29/76 | 3/41 | 38.2 | 92.7 | 7.82 | 2.21–27.64 | < 0.01 |
| Anti-CarP-FCS | 20/76 | 2/41 | 26.3 | 95.1 | 6.96 | 1.54–31.50 | < 0.01 |
| Anti-CarP-Fib | 12/76 | 2/41 | 15.8 | 95.1 | 3.66 | 0.78–17.23 | 0.08 |
| Anti-CCP2 and/or ≥ 1 RF* | 48/76 | 9/41 | 63.2 | 78.1 | 6.10 | 2.54–14.61 | < 0.01 |
| Anti-CCP2 and/or ≥ 1 RF* and/or anti-CarP-FCS | 49/76 | 11/41 | 64.5 | 73.2 | 4.95 | 2.15–11.41 | < 0.01 |
| Anti-CCP2 and/or ≥ 2 RF* | 41/76 | 3/41 | 53.9 | 92.7 | 14.84 | 4.21–52.25 | < 0.01 |
| Anti-CCP2 and/or ≥ 2 RF* and/or anti-CarP-FCS | 43/76 | 5/41 | 56.6 | 87.8 | 9.38 | 3.32–26.53 | < 0.01 |
RA cases positive for RF and/or CCP2 sample n = 166, avg. sample/subject = 2.5; controls sample n = 135, avg. sample/subject = 3.3.
↵† Contains the following statistics: SN and SP.
↵* Count of RF by Neph and RF isotypes (IgM, IgG, IgA). RA: rheumatoid arthritis; RF: rheumatoid factor; Neph: nephelometry; IgM: immunoglobulin M; anti-CCP2: anticyclic citrullinated peptide antibodies version 2; anti-CarP: anti-carbamylated protein; FCS: fetal calf serum; Fib: fibrinogen; SN: sensitivity; SP: specificity; +/n: n positive over the case/control group size; NA: OR, 95% CI, and p cannot be calculated because no controls met positivity criteria.