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AB1259 Comparison of two assays for the determination of anti-citrullinated peptide antibodies (ACPA) using a routine patient cohort
  1. A. Swart1,
  2. G. Lakos2,
  3. J. Wu2,
  4. I. Gürtler3,
  5. M. Mahler2
  1. 1Center for Rheumatic Diseases, Neuss, Germany
  2. 2Research, Inova Diagnostics, San Diego, United States
  3. 3Research, Center for Rheumatic Diseases, Neuss, Germany


Background Anti-citrullinated peptide antibodies (ACPA) are an important serological marker in the diagnosis of rheumatoid arthritis (RA). A variety of different test systems are available for ACPA detection.

Objectives This study compares two ACPA assays in samples sent for routine testing in a clinic specialized in rheumatology. Special objective is to compare the two assays in Rheumatoid factor (RF) negative and early RA.

Methods 295 sera were collected from patients for whom a CCP test was ordered. Samples were tested for ACPA by QUANTA Lite® CCP 3 (INOVA Diagnostics, Inc., San Diego, CA, USA) and EliA® CCP (Phadia, Germany). RF was determined using turbidimetry and RF(II) (Biokit, Spain).

Results Good qualitative (96.6%, kappa= 0.93) and quantitative agreements (Spearman rho=0.77; p<0.0001) were observed between the two tests. Seven samples were CCP3+/CCP2- and one sample was CCP2+/CCP3-. Of the 9 CCP3+/CCP2- patients, 6 (66.7%) had RA, one patient had ankylosing spondylitis, one osteoarthritis and one psoriasis arthritis. The CCP3-/CCP2+ patient had juvenile RA. At the manufacturer’s cut-offs, the sensitivities and specificities were 77.3/98.1% (CCP2), 81.6%/96.8% (CCP3) and 65.2%/89.6% (RF), respectively. At a cut-off which yields 99% specificity, the sensitivities were 59.6% (CCP2) and 69.5% (CCP3). 49/141 (34.8%) RA patients were RF negative. The mean age and the average disease duration were 62.3 years (standard deviation, SD=12.0) and 8.5 years (SD=8.8), respectively. The sensitivities were 49.0% (CCP2) and 57.1% (CCP3) in the RF negative group and 38.7% (CCP2) and 51.6% (CCP3) in the RF negative and early RA (disease duration <5 years; n=31).

Conclusions A good overall agreement between CCP2 and CCP3 was observed. Discrimination between RA and non-RA cases was better using CCP3, especially in early and RF negative RA. Both ACPA assays outperformed RF. Further studies, preferrentially in a uniform multi-center design, are needed to confirm the higher sensitivity of CCP3 in early and RF negative RA.

Disclosure of Interest A. Swart: None Declared, G. Lakos Employee of: INOVA, J. Wu Employee of: INOVA, I. Gürtler: None Declared, M. Mahler Employee of: INOVA

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