Definition
- Antibodies to citrullinated proteins are markers of RA, especially for early diagnosis of the disease. In some cases, these antibodies may be detected many years before the onset of the first symptoms. Other names: CCP-IgG, citrullinated antibody, anticitrullinated antibody, anticitrullinated protein antibody (ACPA).
- Normal range:
- Less than 20 U: negative
- 20 " 39 U: weak positive
- 40 " 59 U: moderate positive
- ≥60 U: strong positive
Use
- Evaluating patients suspected of having RA. The 2010 American College of Rheumatology guidelines recommend performing at least one serologic test (RF or CCP-IgG) and one acute-phase response measure (ESR or CRP) to classify a patient as having or not having definite RA in addition to a history of symptom duration and a thorough joint evaluation.
- Differentiating RA from other connective tissue diseases that may present with arthritis and may be positive for RF, such as HCV-associated cryoglobulinemia, undifferentiated polyarthritis, and Sj ¶gren syndrome.
- Differential diagnosis of early polyarthritis.
Interpretation
- Increased in RA (a positive result for CCP antibodies indicates a high likelihood of RA).
Limitations
- The sensitivity of CCP-IgG for RA varies from about 50 " 75%, depending on the assay and study population, whereas specificity for RA is relatively high, usually >90%.
- Not all individuals with RA will have detectable anti-CCP antibodies, and elevated anti-CCP antibodies may be seen in individuals with no evidence of clinical disease.
- The use of anti-CCP antibody levels for monitoring the progression and/or remission of RA has not been established.
- The diagnostic value of anti-CCP antibodies has not been determined for juvenile arthritis.
Suggested Reading
1Aletaha D, Neogi T, Silman A 2010 Rheumatoid arthritis classification criteria: an American College of Rheumatology/European League Against Rheumatism collaborative initiative. Ann Rheum Dis. 2010;69(9):1580 " 1588.