| Objective: Rheumatoid arthritis (RA) is the most frequent autoimmune rheumatic disease, and can lead to severe disability. The current therapeatic strategy uses increasingly aggressive regimens early in the course of the disease. Thus, early diagnosis is crucial. The diagnosis of RA depends primarily on clinical manifestations, and IgM Rheumatoid factor (RF), witch has a low specificity because it may be found in healty elderly individuals and patients with other autoimmune diseases. The shortcomings of the RF assays have provided impetus for identification of other serological assays for RA. Other autoantibody-antigen systems described in RA are anti-Sa, antikeratin antibodies (AKA) , antiperinuclear factor (APF) . Recently, analysis of AKA and APF autoantibodies showed that most of the reactivity present against these antigens was dircted against citrulline residues, a post-translational modification of the amino acid arginine. This discovery led to the devolopment of assays employing cyclic citrullinated peptides (CCP) to measure antibodies recognizing citrullinated antigens as a diagnostic test for RA. Recent results have shown that Anti-CCP seem be highly specific for RA, and that may possibly be of prognostic value, Anti-CCP positivity showed the strongest association with erosive arthritis. In this study, we evaluated the diagnostic and analytical performances of a new commercial ELISA for the detection of Anti-CCP antibodies. Analyzed the diagnostic value of Anti-CCP in RA, especially in early RA. And we detected AKA, RF, learning the correlation of the three antibodies.Methods: 1. One hundred and twenty serum samples were divided into four groups: (1) Group A, the typical RA (2) Group B, the early RA (Their disease durations were no more than one year and they had no bone erosion in X-ray.) (3) Group C, non RA control (other connective tissue disease except RA) (4) Group D, the healthy control. 2. Anti-CCP activity was determined by an enzyme linked immunosorbent assay (ELISA) using a commercial anti-ccp2 assay provided by Germen Euroimmum com. AKA was detected by indirect immunofluorescence (IIF) technique. 3. statistical analysis was performed using the SAS 6.2 statistical software: A X2 test was used to compare percentages, compared the levels of Anti-CCP in four groups with analysis of variance. Correlation between Anti-CCP and other index was assessed by spearman's correlation analysis.Results: (1) Anti-CCP's positive rate is 70.00% in group A, 83.33% in group B, 6.66% in group C and 0.00% in group D. (2) The serum level of Anti-CCP in four group: group A was 314.08±318.47RU/ml, group B was 135.24±166.59RU/ml, group C was 2.93±1.35 RU/ml, group D was 1.64±1.11 RU/ml. We found there were significant difference (p<0.05) in group A and B, A and C, A and D, B and C, B and D, but no significant difference in group C and D (p>0.05). (3) The sensitivity and specificity of Anti-CCP for RA were 76.67% and 96.62%, positive predictive value (PPV) is 95.83%, negative predictive value (NPV) is 80.56%. The presence of both Anti-CCP and RF increased testing specificity for diagnosis of RA to 96.67%, but sensitivity was 43.33%. The presence of both Anti-CCP, RF and AKA increased the specificity for diagnosis of RA to 98.33%, but decreased the sensitivity to 28.33%. (4) In the early RA cohort of 30 patients, 25/30 (83.33%) were Anti-CCP positive. And 18 of 21 sera negative for RF were positive for Anti-CCP ELISA (85.71%). The positive of the early RA group were higher than the typical RA group, but no distinctive difference (P<0.05). (5) The RA patients with Anti-CCP antibody were significantly different from the patients without antibody in CRP, ESR and PLT (p<0.05).(6) We detected Anti-CCP in RA's synovia of nine patients, 5/9 were Anti-CCP positive.(7) There was significant difference (p<0.05) between the positive of Anti-CCP and AKA , Anti-CCP and RF. Anti-CCP was associated with AKA, RF, ESR, PLT and CRP. (8) Anti-CCP antibody concentration increased according to X-ray grades , but the...
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