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Anti-citrullinated peptide antibodies (ACPA) have a very high specificity for rheumatoid arthritis, much more than that of the rheumatoid factor. In addition, ACPA can be found in sera in the pre-clinical phase, are associated with more severe joint destruction and with higher disease activity. In recent years, keeping pace with new knowledge and with progress made in the antigenic composition of tests and in the characterization of immunogenic epitopes, many immunoenzymatic (ELISA) methods of second and third generation have been produced and marketed commercially, and their use has spread among clinical laboratories. Today, completely automated methods are also available, which are easy to use and with a higher throughput, rendering the diagnostic utility of testing ever faster and more effective. This review takes into consideration the more important characteristics of the new ACPA-ELISA tests now commercially available, and also considers recent progress in standardizing test results.

Joint involvement in systemic sclerosis (SSc) commonly occurs as arthralgias, while a true arthritis is less frequent. The most common arthritis developing in SSc is rheumatoid arthritis (RA) and its diagnosis may be misled by concomitant joint contracture or tendon sheath involvement due to SSc. Anti-citrullinated cyclic peptide (CCP) antibodies are an emerging tool to diagnose RA and have shown to be more specific than rheumatoid factor. We assessed the prevalence of anti-CCP antibodies in SSc patients and evaluated their sensitivity and specificity for associated RA. Searching for RF and anti-CCP antibodies and joint examination were carried out in sixty consecutive SSc patients. Hands and feet standard x-rays were performed in patients complaining with arthralgia and/or arthritis. Six out of sixty (10%) SSc patients had RA according to 1987 ARA revised criteria. Anti-CCP were detected in 5 patients (sensitivity 83%) and RF was present in all RA patients (sensitivity 100%). However, anti-CCP antibodies had a much higher specificity (94%) than RF (41%) for RA. Our study suggests that anti-CCP antibodies are a useful test to identify patients with SSc having also RA. This is crucial in the management of SSc because may allow an adequate therapy of RA and prevent further joint damage in patients who already have a poor quality of life.