kjlm The Korean Journal of Laboratory Medicine Korean J Lab Med 2383-5702 2383-5710 The Korean Society for Laboratory Medicine 10.3343/kjlm.2008.28.6.457 kjlm-28-457 Original Article Diagnostic Utility of AxSYM Anti-Cyclic Citrullinated Peptide Antibody Assay KimKyung-EunM.D. 1 KimKyeong-HeeM.D. 1 WooKwang-SookM.D. 1 HanJin-YeongM.D. 1 KimJeong-ManM.D. 1 LeeSung WonM.D. 2 ChungWon TaeM.D. 2 Department of Laboratory Medicine, Dong-A University College of Medicine, Busan, Korea Department of Internal Medicine, Dong-A University College of Medicine, Busan, Korea Corresponding author: Kyeong-Hee Kim, M.D. Department of Laboratory Medicine, Dong-A University College of Medicine, 1 Dongdaesindong 3-ga, Seo-gu, Busan 602-103, Korea Tel: +82-51-240-2850, Fax: +82-51-255-9366 E-mail: progreen@dau.ac.kr 022008 14022008 286 457464 23052008 18092008 29092008 Copyright © 2008 by the Korean Society for Laboratory Medicine 2008 This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. 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.

 Conclusions

Diagnostic performance of automated AxSYM anti-CCP assay was comparable to that of DIASTAT 96 well plate ELISA method. AxSYM anti-CCP assay has an advantage of random access capability and will be useful in laboratories with low sample number and/or with a need of rapid turnaround time.

 Anti-cyclic citrullinated peptide antibody Rheumatoid factor Rheumatoid arthritis AxSYM immunoassay REFERENCES Kasper DL Fauci AS eds. Harrison's principles of internal medicine 16th ed. New York McGraw-Hill 2004196876 Boers M Verhoeven AC Markusse HM van de Laar MA Westhovens R van Denderen JC Randomised comparison of combined step-down prednisolone, methotrexate and sulphasalazine with sulphasalazine alone in early rheumatoid arthritis Lancet 1997350 30918 Anderson JJ Wells G Verhoeven AC Felson DT Factors predicting response to treatment in rheumatoid arthritis: the importance of disease duration Arthritis Rheum 200043 229 Steiner G Smolen J Autoantibodies in rheumatoid arthritis and their clinical significance Arthritis Res 20024 S S15 Arnett FC Edworthy SM Bloch DA McShane DJ Fries JF Cooper NS The American Rheumatism Association 1987 revised criteria for the classification of rheumatoid arthritis Arthritis Rheum 198831 31524 Schellekens GA Visser H de Jong BA van den Hoogen FH Hazes JM Breedveld FC The diagnostic properties of rheumatoid arthritis antibodies recognizing a cyclic citrullinated peptide Arthritis Rheum 200043 15563 van Boekel MA Vossenaar ER van den Hoogen FH van Venrooij WJ Autoantibody systems in rheumatoid arthritis: specificity, sensitivity and diagnostic value Arthritis Res 20024 8793 Nishimura K Sugiyama D Kogata Y Tsuji G Nakazawa T Kawano S Meta-analysis: diagnostic accuracy of anti-cyclic citrullinated peptide antibody and rheumatoid factor for rheumatoid arthritis Ann Intern Med 2007146 797808 Clinical and Laboratory Standards Institute Evaluation of the linearity of quantitative measurement procedures: a statistical approach; approved guideline. Document EP6-A Wayne PA Clinical and Laboratory Standards Institute 2003 Clinical and Laboratory Standards Institute Evaluation of precision performance of quantitative measurement methods; approved guideline-2nd edi. Document EP5-A2 Wayne PA Clinical and Laboratory Standards Institute 2004 Newkirk MM Rheumatoid factors: host resistance or autoimmunity? Clin Immunol 2002104 113 Avouac J Gossec L Dougados M Diagnostic and predictive value of anti-cyclic citrullinated protein antibodies in rheumatoid arthritis: a systematic literature review Ann Rheum Dis 200665 84551 Nielen MM van Schaardenburg D Reesink HW van de Stadt RJ van der Horst-Bruinsma IE de Koning MH Specific autoantibodies precede the symptoms of rheumatoid arthritis: a study of serial measurements in blood donors Arthritis Rheum 200450 3806 van Oosterhout M Bajema I Levarht EW Toes RE Huizinga TW van Laar JM Differences in synovial tissue infiltrates between anti-cyclic citrullinated peptide-positive rheumatoid arthritis and anti-cyclic citrullinated peptide-negative rheumatoid arthritis Arthritis Rheum 200858 5360 Liao KP Batra KL Chibnik L Schur PH Costenbader KH Anti-cyclic citrullinated peptide revised criteria for the classification of rheumatoid arthritis Ann Rheum Dis 200867 155761 Lutteri L Malaise M Chapelle JP Comparison of second- and third-generation anti-cyclic citrullinated peptide antibodies assays for detecting rheumatoid arthritis Clin Chim Acta 2007386 7681 Coenen D Verschueren P Westhovens R Bossuyt X Technical and diagnostic performance of 6 assays for the measurement of citrullinated protein/peptide antibodies in the diagnosis of rheumatoid arthritis Clin Chem 200753 498504 Cho SY Kang SY Lee HJ Lee WI A comparative evaluation of the diagnostic value of anti-cyclic citrullinated peptide and rheumatoid factor in rheumatoid arthritis Korean J Lab Med 200828 3945 (조선영, 강소영, 이희주, 이우인. 류마티스 관절염 진단에 있어서 항-Cyclic Citrullinated Peptide 항체와류마티스인자의진단적가치비교평가. 대한진단검사의학회지 2008;28: 39-45.) Salvador G Gomez A Vinas O Ercilla G Canete JD Munoz-Gomez J Prevalence and clinical significance of anti-cyclic citrullinated peptide and antikeratin antibodies in palindromic rheumatism An abortive form of rheumatoid arthritis? Rheumatology 200342 9725 Russell AS Devani A Maksymowych WP The role of anti-cyclic citrullinated peptide antibodies in predicting progression of palindromic rheumatism to rheumatoid arthritis J Rheumatol 200633 12402 Chan MT Owen P Dunphy J Cox B Carmichael C Korendowych E Associations of erosive arthritis with anti-cyclic citrullinated peptide antibodies and MHC Class II alleles in systemic lupus erythematosus J Rheumatol 200835 7783 Figures and Tables

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.

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.

Linearity of AxSYM anti-CCP antibody test. Abbreviation: CCP, cyclic citrullinated peptide.

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

Abbreviations: RA, rheumatoid arthritis; M, male; F, female.

Distribution of positivities of two anti-CCP tests

    DIASTAT anti-CCP
Positive Negative
RA (n=52)      
 AxSYM anti-CCP Positive 41 2
  Negative 3 6
Non-RA (n=73)      
 AxSYM anti-CCP Positive 11 3
  Negative 2 57
Healthy control (n=47)      
 AxSYM anti-CCP Positive 0 0
  Negative 1 46

Abbreviations: CCP, cyclic citrullinated peptide; RA, rheumatoid arthritis.

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

  DIASTAT AxSYM RF
Manufacturer's cut-off 5 U/mL 5 U/mL 18 IU/mL
 Sensitivity 84.6% 82.7% 78.8%
 Specificity 88.3% 88.3% 72.5%
Cut-off based on ROC 2.4 U/mL 8.4 U/mL 27.2 IU/mL
 curves      
 Sensitivity 86.5% 80.8% 76.9%
 Specificity 88.3% 93.3% 84.2%

Abbreviations: CCP, cyclic citrullinated peptide; RA, rheumatoid arthritis; RF, rheumatoid factor.

Precision of AxSYM anti-CCP test

  N Mean (U/mL) SD Within-run CV (%) Total CV (%)
Positive control 20 20.21 1.05 3.4 5.2
Pooled negative serum 20 1.27 0.12 9.3 9.8

Abbreviation: CCP, cyclic citrullinated peptide.