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Abstract
Background
The presence of rheumatoid factor (RF) is one of the classification criteria of the American College of Rheumatology (ACR) for rheumatoid arthritis (RA), but it has a limitation of low specificity. We compared the diagnostic utility of anti-cyclic citrullinated peptide (CCP) antibodies analyzed by an automated immunoassay system with that measured by a 96 well plate ELISA method.
Methods
The RF and anti-CCP antibodies were determined in 172 serum samples: 52 RA patients, 73 disease controls (systemic lupus, Sjogren's syndrome, palindromic rheumatism), and 47 healthy controls. Anti-CCP antibodies were measured by DIASTAT 96 well plate ELISA method (Axis-Shield Diagnostics, UK) and AxSYM automated microparticle enzyme immunoassay system (Abbott Laboratories, USA). RF was assayed by latex immunoturbidimetry (Toshiba 200 FR, Japan). The diagnostic performances of these tests were compared using a ROC curve analysis, and linearity and precision analysis of AxSYM anti-CCP was carried out.
Results
The sensitivities of RF, DIASTAT anti-CCP, and AxSYM anti-CCP were 78.8%, 84.6%, and 82.7%, respectively and the specificities were 72.5%, 88.3%, and 88.3%, respectively. On ROC curve analysis, the area under the curve was 0.924 for AxSYM anti-CCP, 0.886 for DIASTAT anti-CCP, and 0.847 for RF. AxSYM anti-CCP showed a good linearity, and within-run and total-run precision.
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Fig. 1.
Distribution of the test results according to the concentrations of anti-CCP antibodies and RF for different groups of patients. Line: cut-off values ([A] DIASTAT, 5 U/mL; [B] AxSYM, 5 U/mL; [C] RF, 18 IU/mL).
Abbreviations: CCP, cyclic citrullinated peptide; RF, rheumatoid factor; HC, healthy control; OA, osteoarthritis; PR, palindromic rheumatism; RA, rheumatoid arthritis; SLE, systemic lupus erythematosus.
Fig. 2.
The receiver operator characteristics (ROC) curves of Dia-STAT anti-CCP (AUC, 0.888), AxSYM anti-CCP (AUC, 0.923) and RF (AUC, 0.847) in RA patients and control group. There was no significant difference among the AUCs.
Abbreviations: Sen, sensitivity; Spe, Specificity; CCP, cyclic citrullinated peptide; RF, rheumatoid factor; RA, rheumatoid arthritis; AUC, area under the curve.
Table 1.
The characteristics of rheumatoid arthritis patients and control subjects
| N of subjects | Age (Mean±SD) | M/F | |
|---|---|---|---|
| RA | 52 | 50.2±12.5 | 9/43 |
| Control diseased healthy | 73 | 45.7±14.5 | 21/52 |
| 47 | 45.5±9.8 | 28/19 |
Table 2.
Distribution of positivities of two anti-CCP tests
Table 3.
Comparison of sensitivities and specificities of DIASTAT anti-CCP, AxSYM anti-CCP and RF tests in RA patients and control group using the manufacturer's cut-off values and ROC curves derived cut-off values
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