Background
Rheumatoid factor (RF) is found in patients with systemic lupus erythematosus (SLE). Anti-citrullinated peptide antibodies (ACPA) are more specific for rheumatoid arthritis than RF.
Objective
Our aim was to determine the prevalence of RF and ACPA in SLE patients.
Methods
In this study, samples from 201 consecutive patients diagnosed with SLE and fulfilling ACR criteria were used. Fine ANA reactivities were tested by INNO-LIA™ ANA (Innogenetics, Gent, Belgium) and by IIF on C. luciliae. RF was detected by latex fixation. ACPA were detected by anti-CCP2 ELISA (Euro-Diagnostica, Arnhem, The Netherlands) and by a research INNO-LIA™ RA (Innogenetics, Gent, Belgium) for the detection of anti-pepA and anti-pepB antibodies. The prevalences of ACPAwere compared by the McNemar test.
Results
RF at a titre ≥160 was found in 26 patients (13.0%). ACPA were found in 16 samples (Table 1). The prevalence of anti-CCP2 antibodies was significantly higher than that of anti-pepA antibodies (P = 0.001) and anti-pepB antibodies (P = 0.022).
Table 1.
Characteristics of ACPA-positive SLE patients
| RF (titre) | Anti-CCP2 (U/ml; cut-off 25 U/ml) | Anti-pepA | Anti-pepB | ANA fine reactivities | |
|---|---|---|---|---|---|
| 1 | 1280 | 186 | + | + | Ro60, SSB |
| 2 | 0 | 28 | - | - | SmB, SmD, histones, dsDNA |
| 3 | 640 | 9 | - | + | RNP-C |
| 4 | 0 | 168 | - | - | dsDNA |
| 5 | 0 | 53 | - | - | SmB, dsDNA |
| 6 | 80 | 2 | - | + | Histones, dsDNA |
| 7 | 0 | 76 | - | - | SmB, RNP-A, RNP-C, RiboP, histones |
| 8 | 40 | 64 | - | - | SmD, SmB, RNP-70k, RNP-C, RiboP |
| 9 | 0 | 58 | - | - | - |
| 10 | 320 | 110 | - | - | SmB, RNP-70k, RNP-A, RNP-C, Histones, dsDNA |
| 11 | 0 | 28 | - | - | - |
| 12 | 0 | 36 | - | - | - |
| 13 | 320 | 78 | + | + | SmB, RNP-70k, RNP-A, RNP-C |
| 14 | 80 | 56 | - | - | RNP-A, RiboP, Histones |
| 15 | 640 | 52 | - | - | RNP-70k, RNP-A |
| 16 | 320 | 1600 | + | + | Ro60 |
Conclusion
RF is found in 13.0% of SLE patients. Anti-CCP2 antibodies are false-positive in 7.0% (n = 14) of SLE patients, which occurs significantly more often than anti-pepA (1.5%, n = 3) and anti-pepB (2.5%, n = 5) antibodies.