All you wanted to know about anti-CCP but were afraid to ask.

The most specific biomarker associated with the diagnosis of rheumatoid arthritis (RA) is autoantibodies to citrullinated peptides/proteins (ACPA). Though recognized as an important marker of progressive erosive disease its use has been hampered by doubt about what is a positive versus a negative reaction in the several assays that have become available commercially. This review intends to indicate that the CCP2 assay has the highest specificity and sensitivity in stratified studies that encompass sera from RA patients and non-RA inflammatory controls compared to other ACPA tests. Still, larger and strictly stratified studies are highly warranted to substantiate this conclusion.