Journal Article

High positive predictive value of specific antibodies cross-reacting with a 28-kDa Drosophila antigen for diagnosis of ankylosing spondylitis

C. Duftner, C. Dejaco, A. Klauser, A. Falkenbach, H. J. Lakomek and M. Schirmer

in Rheumatology

Volume 45, issue 1, pages 38-42
Published in print January 2006 | ISSN: 1462-0324
Published online September 2005 | e-ISSN: 1462-0332 | DOI: https://dx.doi.org/10.1093/rheumatology/kei109
High positive predictive value of specific antibodies cross-reacting with a 28-kDa Drosophila antigen for diagnosis of ankylosing spondylitis

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Objectives. Diagnosis of ankylosing spondylitis (AS) can be difficult, and a specific laboratory test has not yet been introduced as a routine diagnostic tool. Our aim was to evaluate the diagnostic value of antibodies specifically binding to a recombinant 28-kDa antigen for the diagnosis of AS.

Methods. Blinded sera were tested for antibodies binding to the procaryotically expressed 28-kDa protein using an enzyme-linked immunosorbent assay (ELISA). This purified 28-kDa protein is produced by a specific clone from an embryonic Drosophila hydei Xgtl I c-DNA library and is bound by human antibodies cross-reacting with both a 36-kDa protein of chromosomes from Drosophila melanogaster and a 69-Da HeLa S3 protein potentially involved in signal transduction pathways.

Results. Serum concentrations of antibodies cross-reacting with this specific antigen were increased in 371 patients with AS compared with 37 healthy controls (39.5 vs 22.6 U/ml; P = 0.004). The positive predictive values of this ELISA test for AS were between 95.1% (95% confidence interval 90.6–97.9%) for a cut-off level of 50 U/ml and 97.4% (92.7–99.5%) for a cut-off level of 75 U/ml, and the sensitivities were between 42.1% (37.0–47.3%) for a cut-off level of 50 U/ml and 30.7% (26.1–35.7%) for a cut-off level of 75 U/ml.

Conclusions. Serum ELISA tests for antibodies cross-reacting with the 28-kDa antigen show a high positive predictive value for AS of more than 95%.

Keywords: Ankylosing spondylitis; Diagnostic test; Immunoassay; Antibodies

Journal Article.  3354 words.  Illustrated.

Subjects: Radiology ; Rheumatology

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