Egyptian Journal of Medical Microbiology October 2012 - PDF document

Egyptian Journal of Medical Microbiology, October 2012 Vol. 21, No. 4 ide (ACCP) Antibody versus Rheumatoid Factor (RF) For Di, Hoda M. Moghazy, Ahmed M. BoghdadyAhmed HassanDepartments of Medical Microbiology and Immunology, Egyptian Journal of Medical Microbiology, October 2012 Vol. 21, No. 4 own proteins) that are frequently detected in the blood of rheumatoid arthritis patients. The main epitope for these antibodies is filaggrin, and there is cross-reactivity between ACPA and anti-keratin and anti-perinuclear factor During inflammation, arginine residues in proteins such as vimentin can be enzymatically converted into citrulline ones (a process called citrullination), and, if their shapes are significantly altered, the proteins may be seen as antigens by the immune system, thereby generating an immune response. ACPAs have proved to be powerful biomarkers for the diagnosis of rheumatoid arthritis (RA) at a very early stage. In July 2010, the 2010 ACR/EULAR Rheumatoid Arthritis Classification Criteria were introducedinclude ACPA testing, and overruled the "old" ACR criteria of 1987 and are adapted for early RA diagnosis.AIM OF THE WORKThe aim of this study was to compare the diagnostic power of anti-cyclic citrullinated peptide (ACCP) antibody to rheumatoid factor (RF) in RA adult patients. MATERIAL & METHODSThis study was carried out in the Medical Microbiology and Immunology Department, Faculty of Medicine, Sohag University. Blood samples were collected from 180 patients (144 female and 36 males their age ranged from 19-65 years), who had been attending the outpatient clinic of Rheumatology and Rehabilitation Department from October 2011 to January 2012. All of them were complaining of joint pain. Anti- CCP IgG and RF IgM were estimated by ELISA technique [Axis – shield diagnostics limited the technology park, Dundee- United Kingdom] according to manufacturer's instructions. The cut-off value was set as leve�ls 20 IU/ml for RF and leve�ls 5 IU/ml for ACCP were considered positive. Statistical Analysis: Data analysis was performed using SPSS statistical software (version 9 Chicago IL, USA). The sensitivity and specificity were calculated for anti-CCP and RF. In order to compare the clinical characteristics in subgroups of RA patients positive or negative for anti-CCP antibodies and RF, 2 test was used for categorical variables. Student t test was used to compare means. Pwas considered significant. The characteristics of the 180 patients are summarized in Table (1). Patients were classified as RA and non-RA. More than one rheumatologist confirmed the diagnosis of all 31 RA patients according to the ACR criteria Table 1: Characteristics of the 180 patients, data are presented as counted (percentages) and as mean ± (n= 31) (17%)(83%)Total DiagnosisP value Female 119 Age (mean ± SD) 41.1 ± 14.17 40.5 ± 12.62 0.834 The overall prevalence of RA in this study was 17%. The ratio of female to male was 4:1 for both the RA and no

n-RA groups. Results of ACCP antibodies and RF in both RA and non-RA patients are summarized in Table (2). Table 2: Results of ACCP antibodies and RF in both RA and non-RA.RA n = 31nRA n = 149 RA ACCPACCP positive ACCP negativeACCP positive ACCP negative RF positive RF negative 17 2 3 9 1 14 3 131 Egyptian Journal of Medical Microbiology, October 2012 Vol. 21, No. 4 Test properties of ACCP antibodies and RF are shown in Table (3), using the cut offs between positive and negative recommended by the manufacturers. Statistically significant and accuracy were obtained for ACCP antibodies than for RF. There was statistically non-significant higher sensitivity for ACCP antibodies than for RF. Levels above the 5 U/ml cutoff yielded a LR of 23.89 for ACCP antibodies; levels above the 20 IU/ml cutoff showed a LR of 6 for RF. This means that RA patients are 23.89 or 6 times more likely to have a positive anti-CCP or RF test, respectively than non-RA patients. Accuracy of ACCP antibodies is statistically significant higher than that of RF. The sensitivity of ACCP antibodies for RA was 64.5%, while it was 61.3% for RF (Table 3). Including patients who were positive for either test increased the sensitivity of the serologic tests to 71%. The specificity of ACCP antibodies was 97.3% compared to 90% for RF (Table 3), while it was 99% when both were positive (not shown). Table 3: Tests properties of anti-CCP antibodies and RF. ACCP RF P vale Sensitivity Pretest probability PPV positive predictive value, NPV negative predictive value, LR + positive likelihood ratio, LR – negative likelihood ratio. LRs and disease probability after combining RF and ACCP antibodies, plus their relationship to each other, are shown in (Tables 4) using the cut offs recommended by the manufacturers. When both tests are negative, there is nearly a threefold decrease in the likelihood of having RA, down to 6%. The ACCP-negative/RF-positive combination showed no significant change from the pretest to posttest probability of having RA. This is related to the finding mentioned above that RF levels are not different in ACCP-negative RA patients and non-RA patients. A positive anti-CCP test combined with a negative RF yielded a mild increase in the probability of RA. When both tests are positive, there is a very high LR (43.4) and PTP of RA (90%). More than half of the RA patients (54% Table 2) were double positive for these serologic markers. Table 4: Disease probability after combination of RF, ACCP antibody and LR.Test combinationLikelihood ratio% posttest probability ACCP negative/ RF negative ACCP negative/ RF positive ACCP positive/ RF negative ACCP positive/ RF positive DISCUSSIONThis study evaluated the clinical utility of the anti- CCP test in comparison with RF for the diagnosis of RA. Rheumatoid arthritis (RA) is one of the most prevalent autoimmune diseases, affecting up to 1% of some populations. Our results showed that the ratio of RA was 17 % from joint disease in the studied cases, which is consistent with previous

researches(17,18). It affects about 4 times as many women as men. A small non- significant difference was found in age between RA and non RA groups. This is in agreement with other reports. Early diagnosis of RA is an important consideration because aggressive therapy can prevent the development of articular erosions and deformities. At present, the Egyptian Journal of Medical Microbiology, October 2012 Vol. 21, No. 4 diagnosis of RA is still defined by the 1987 criteria of the ACR in most of the hospitalsHowever, these classification criteria have low sensitivity in early RA(21,22) Therefore, a more specific and sensitive marker for the diagnosis of RA should be developed that ideally can be used to detect RA at the early stage of the disease. RF had a good sensitivity but not very good specificity in the diagnosis of RA. However, ACCP antibodies had equal sensitivity and much better specificity and was, thus, even more clinically useful. The results of this study showed that, there was statistically non significant increase in the sensitivity of ACCP over that of RF (64.5% versus 61.3%). There was statistically significant increase in the specificity of ACCP antibodies over that of RF (97.3% versus 90%), these results were in agreement with others In a recent review, Pruijn et al. had calculated the cumulative sensitivity and specificity (71.6% and 95.3%, respectively) of the ACCP test based on the results of 154 independent studies published between 2002 and June 2009. To explain the low sensitivity of ACCP antibodies, it must be considered that ACCP antibodies are a heterogeneous group of antibodies directed against different epitopes on the citrulline molecule, that each patient’s serum contains different subsets of antibodies, and that the synthetic peptide used in this assay represents a relatively small set of antigenic determinants that do not entirely encompasses the antigenic determinants present on the as yet unknown antigenic molecule in the jointRF alone is not always indicative of RA since RF is detected in many other autoimmune diseases. When testing with RF alone, RA patients may not be diagnosed early enough to prevent irreversible damage. Prognostic assessment at the time of first presentation is crucial, particularly given the new therapeutic approaches for early RA patients. In line with a previous study by Moghimi et al. 2012, our study demonstrated the presence of ACCP antibodies in significant numbers of RF-negative RA patients. It, therefore, seems advantageous to request ACCP antibodies test in patients with arthritis who have negative RF. Out of the 12 RF seronegative patients 3 were positive for ACCP antibodies. Therefore, a positive ACCP antibody supports the diagnosis of RA when RF is negative in the appropriate clinical setting. Thus, anti-CCP antibody serves as a better diagnostic marker in the diagnosis of RA, especially to detect the seronegative group. This result is supported by reports of others Combining ACCP antibodies and RF results, using the cut offs reco

mmended by the manufacturers result, is higher diagnostic power than using either of the tests alone because there is an increase in sensitivity when either is positive and an increase in specificity when both are positive, compared to either marker alone. In this study, the sensitivity of ACCP antibodies for RA was 64.5%, while it was 61.3% for RF. Including patients who were positive for either test increased the sensitivity of the serologic tests to 71%. The specificity of anti-CCP was 97.3% compared to 90% for RF, while it was 99% when both were positive. When both tests are negative, there is nearly a threefold decrease in the likelihood of having RA, down to 6%. A positive anti- CCP test combined with a negative RF yielded a mild increase in the probability of RA. When both tests are positive, there is a very high LR (43.4) and PTP of RA (90%). Some reports suggest that RF and ACCP antibodies should be combined to reach the optimum diagnostic properties(25,28,32,33) whereas others find only a little additional diagnostic value when combining RF and ACCP antibodiesset of criteria is made to classify early RA, ACCP antibodies should be included because it would increase the diagnostic power of serologic tests compared to RF alone. Only 4 patients in this study were ACCP antibodies positive without a diagnosis of RA, and one of them was also positive for RF. Given the high diagnostic utility of ACCP antibodies, if the doctors had known the ACCP antibodies results, it is possible that they would have considered a diagnosis of RA more strongly. Two groups of patients will be particularly interesting to follow in the future. One group is the 4 patients who were not diagnosed with RA but were positive for ACCP antibodies, with or without concomitant RF, to see if any of them will develop RA. At least one study by (Rantapaa-Dahlqvist et al. 2003) has shown that ACCP antibodies can appear up to several years in advance of diagnosis of RA. The other is the group of 9 RA patients that were double negative for the serologic markers to see if this group has a very mild disease than the patients who were positive for the serologic markers. REFERENCE Van Venrooij, W. J., Van Beers, J. J., and Pruijn, G. J.Anti-CCP Antibody, a Marker for the Early Detection of Rheumatoid Arthritis. Annals of the New York Academy of Sciences 1143:268-285 Egyptian Journal of Medical Microbiology, October 2012 Vol. 21, No. 4 Silman, A.J., and Pearson, J.E. 2002. Epidemiology and genetics of rheumatoid arthritis. Arthritis Research 4(Suppl 3):S265-S272. Kvien, T.K. 2002. Epidemiology of disability in rheumatoid arthritis. Rheumatology 41(2):121-123. Arnett, F.C., Edworthy, S.M., Bloch, D. A., et al. 1988. The American Rheumatism Association 1987 revised criteria for the classification of rheumatoid arthritis. Arthritis and Rheumatism 31(3):315-324. Möttönen, T.T. 1988. Prediction of erosiveness and rate of development of new erosions in early rheumatoid arthritis. Annals of the Rheumatic Diseases 47(8): Van der He

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