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Open Access Research article

Anti-ribosomal P protein IgG autoantibodies in patients with systemic lupus erythematosus: diagnostic performance and clinical profile

Diana Carmona-Fernandes1, Maria José Santos12, Helena Canhão13 and João Eurico Fonseca13*

Author Affiliations

1 Rheumatology Research Unit, Instituto de Medicina Molecular, Lisbon Academic Medical Centre, Av. Prof. Egas Moniz, Edifício Egas Moniz, Lisboa, 1649-028, Portugal

2 Rheumatology Department, Hospital Garcia de Orta, Av. Torrado da Silva, Pragal, Almada, 2801-951, Portugal

3 Rheumatology and Bone Metabolic Diseases Department, Hospital de Santa Maria, Av. Prof. Egas Moniz, Lisboa, 1649-035, Portugal

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BMC Medicine 2013, 11:98  doi:10.1186/1741-7015-11-98

Published: 4 April 2013

Abstract

Background

This study was devised to assess the performance of anti-ribosomal P (anti-Rib-P) antibodies in the diagnosis of systemic lupus erythematosus (SLE) and the association of these antibodies with the clinical features of SLE.

Methods

We used a fluorescence enzyme immunoassay to determine anti-Rib-P levels in an SLE group, a rheumatic disease control (RDC) group (rheumatoid arthritis (RA), ankylosing spondylitis, psoriatic arthritis and juvenile idiopathic arthritis), and a healthy control (HC) group. We also determined anti-Smith antigen (anti-Sm) and anti-double-stranded DNA (anti-dsDNA) antibody levels. Receiver operating characteristic (ROC) curves were constructed and the best cut-off points for positivity were determined. Using regression analysis, the relationship between clinical variables and autoantibody levels was analyzed.

Results

In total, 127 patients with SLE, 256 controls with other rheumatic diseases, and 100 HCs were studied. Anti-Rib-P autoantibodies were positive in 18 (14.2%) of the patients with SLE (mean concentration of 30.6 ± 46.9 U/ml) and in 2 patients with RA (0.8% of the RDC group). In addition, 12 patients with SLE (9.4%) were positive for anti-Sm (31.1 ± 40.8 U/ml) and 63 (49.6%) were positive for anti-dsDNA autoantibodies (88.4 ± 88.5 U/ml). When we assessed the 18 patients with SLE who had tested positive for anti-Rib-P, we found that 4 of these were positive for anti-Rib-P only, whereas 12 were positive for anti-Rib-P plus anti-dsDNA, and 2 were positive for all three antibodies. There were no samples positive for anti-Rib-P plus anti-Sm. The specificity, sensitivity, positive likelihood ratio, and negative likelihood ratio of anti-Rib-P for SLE diagnosis were 99.4%, 14.2%, 23.7%, and 0.86%, respectively.

Caucasian ethnicity was associated with lower anti-Rib-P antibody levels. No relation was found between anti-Rib-P levels and neuropsychiatric or other clinical features.

Conclusions

Anti-Rib-P autoantibodies have high specificity for SLE, and measurement of these might improve the accuracy of SLE diagnosis. In this study, we found that Caucasian ethnicity was associated with lower anti-Rib-P antibody levels.

Keywords:
Anti-Rib-P; Systemic lupus erythematosus; Antibodies