False positivity of rheumatoid factor and antibodies to citrullinated peptides in systemic lupus erythematosus
Received: 16 January 2004
Published: 24 February 2004
Keywords
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
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.
