RESEARCH - Do all anti-citrullinated protein/peptide antibody tests measure the same?

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Published Online First: 20 July 2007. doi:10.1136/ard.2007.071654

ls of the Rheumatic Diseases 2008;67:542-546

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Do all anti-citrullinated protein/peptide antibody tests measure the

same? Evaluation of discrepancy between anti-citrullinated

protein/peptide antibody tests in patients with and without rheumatoid

arthritis

B Vander Cruyssen 1, L Nogueira 3, J Van Praet 1, D Deforce 2, D

Elewaut 1, G Serre 3, F De Keyser 1

1 Department of Rheumatology, Ghent University Hospital, Gent, Belgium

2 Laboratory of Pharmaceutical Biotechnology, Ghent University, Ghent, Belgium

3 UMR 5165 " Laboratory of Epidermis Differentiation and Rheumatoid

Autoimmunity " , CNRS–Toulouse III University, Toulouse, France

ABSTRACT

Background: Different methods exist to demonstrate anti-citrullinated

protein/peptide antibodies (ACPA).

Aims: To evaluate discrepancy between four ACPA tests.

Patients and methods: Population 1 consisted of patients with a new

diagnostic problem, including 86 patients with rheumatoid arthritis

(RA) and 450 patients without RA. Population 2 consisted of 155

patients with RA who had long-standing disease. Population 3 consisted

of 188 patients with psoriatic arthritis and in population 4 there

were 192 patients with systemic lupus erythematosus. Populations 1 and

2 were tested with the anti-human fibrinogen antibody (AhfibA) test,

anti-CCP2 from Eurodiagnostica (CCP2-euro), anti-CCP2 from Pharmacia

(CCP2-phar) and anti-CCP3 test by Inova (CCP3). Samples were annotated

as discrepant if positive in one and negative in at least one other

test. Each discrepant sample was re-analysed in a different run.

Populations 3 and 4 were analysed in the CCP2-euro and AhFibA test.

Results: In population 1, ACPA positivity was found in 17 of 450

(3.8%) patients without RA; 14 (82%) of these 17 samples were

discrepant. In contrast, 61 of 86 (70.9%) patients with RA were ACPA

positive of whom 18 of 61 (29.5%) were discrepant (70.9% vs. 29.5%,

p<0.001). The discrepancies between tests could be partly attributed

to borderline results, inter-assay discrepancy and inter-test

variability. They were more prevalent in patients with systemic lupus

erythematosus who were ACPA positive than in those with psoriatic

arthritis who were ACPA positive.

Conclusions: Discrepancy between different ACPA tests was observed

attributable to the occurrence of borderline results, inter-assay

variability and mainly to inter-test variability. The lowest

inter-test discrepancy is observed between tests that use the same

substrate.

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Read the entire article here:

http://ard.bmj.com/cgi/content/full/67/4/542

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