| Premorbid sera | Postdiagnostic sera | |||||||||
| Cut-off value | Overall premorbid positivity in RA case sera (n = 49) | Overall premorbid positivity in control sera (n = 245) | Positivity in RA case sera >5 years before diagnosis (n = 30) | Positivity in RA case sera ⩽5 years before RA diagnosis (n = 19) | Positivity in postdiagnostic RA case sera (n = 33) | |||||
| Percentage (n) | Percentage (n) | Percentage (n) | OR (95% CI) | Percentage (n) | OR (95% CI) | Percentage (n) | OR§ (95% CI) | |||
| IgM rheumatoid factor | 17 IU/ml | 20 (10) | 3 (8) | 20 (6) | 9.2 (2.3 to 45.3) | 21 (4) | 5.9 (1.2 to 32.2) | 64 (21) | 96.2 (17.5 to 999) | |
| IgA rheumatoid factor | 25 AU/ml | 21 (10)* | ‡ | 14 (4)† | 32 (6) | 34 (10)† | ||||
| IgG anti-CCP | 25 AU/ml | 31 (15) | 1 (2) | 17 (5) | 33.6 (6.1 to ∞) | 53 (10) | 25.0 (6.1 to 168) | 55 (18) | 45.0 (12.1 to 287) | |
| IgM rheumatoid factor+IgG anti-CCP | 14 (7) | 0 (0) | 10 (3) | 19.2 (2.9 to ∞) | 21 (4) | 26.4 (4.5 to ∞) | 48 (16) | 113 (24.3 to ∞) | ||
| EBNA IgG | 0.250 OD | 88 (43) | 94 (231) | 90 (27) | 0.5 (0.1 to 2.8) | 84 (16) | 0.2 (0.0 to 1.6) | 88 (29) | 0.5 (0.1 to 2.2) | |
| EBV-VCA IgG | 0.250 OD | 92 (45) | 97 (238) | 93 (28) | 0.5 (0.1 to 3.8) | 89 (17) | 0.1 (0.0 to 1.5) | 94 (31) | 0.6 (0.1 to 4.4) | |
| Parvovirus IgG | 0.190 OD | 67 (33) | 65 (159) | 63 (19) | 1.0 (0.4 to 2.5) | 74 (14) | 1.4 (0.4 to 5.3) | 64 (21) | 1.0 (0.4 to 2.4) | |
RA, rheumatoid arthritis; IU, international units; AU, arbitrary units; OD, optical density; EBV, Epstein–Barr virus; EBNA, nuclear antigen of EBV; EBV-VCA, EBV antibody to viral capsid antigen; CCP, cyclic citrullinated peptide.
*n = 48 sera. †n = 29 sera. ‡Antibodies against IgA rheumatoid factor only analysed in cases. §OR estimated by comparing postdiagnostic measurements in RA cases with premorbid measurements in matched controls.