Anti-CCP & Rheumatoid Factor: Rheumatoid Arthritis Tests

Comparing the Two Tests

Non-RA Causes of Positive RF

• Sjögren's syndrome
• SLE (lupus)
• Infection (subacute bacterial endocarditis, hepatitis C, TB)
• Other connective tissue diseases
• Healthy elderly: up to 5% of those >70 years
• Cryoglobulinaemia

References

The clinical information on this page is drawn from peer-reviewed sources indexed by the US National Library of Medicine. Links go to the source so you can read it yourself.

1. Erythrocyte Sedimentation Rate. In: StatPearls. Treasure Island (FL): StatPearls Publishing. NCBI Bookshelf NBK557485

References

Sources cited on this page. PubMed links open the original abstract.

1. Schellekens GA, Visser H, de Jong BA, et al. The diagnostic properties of rheumatoid arthritis antibodies recognizing a cyclic citrullinated peptide. Arthritis Rheum. 2000;43(1):155–163. PMID 10513793 · doi:10.1002/1529-0131(200001)43:1<155::AID-ANR20>3.0.CO;2-3

Why anti-CCP is more specific than rheumatoid factor

Rheumatoid factor (RF) was the first autoantibody discovered in rheumatoid arthritis, but it has significant limitations: it is positive in only 70–80% of RA patients (RF-negative RA exists), and it is also positive in many other conditions – hepatitis C, Sjögren's syndrome, SLE, sarcoidosis, infective endocarditis, and in 5–10% of healthy older adults. This low specificity reduces its diagnostic value.

Anti-CCP antibodies (anti-cyclic citrullinated peptide, also called anti-citrullinated protein antibodies – ACPA) are far more specific for RA: they appear in around 70–75% of RA patients but in fewer than 2% of healthy individuals. Their high specificity (approximately 95–98%) means a positive anti-CCP result is strong evidence for RA, not merely "possible RA".

The two tests complement each other. Approximately 30% of RA patients are seronegative for RF but seropositive for anti-CCP, and vice versa in a small proportion. Measuring both together maximises sensitivity – a patient positive for either or both has a high probability of RA. Positivity for both simultaneously is found in about 50–60% of RA patients and is associated with more aggressive disease and greater joint damage.

Anti-CCP and prognosis – predicting joint damage

Anti-CCP antibodies can appear in the bloodstream 5–10 years before clinical symptoms of RA develop. This pre-clinical window has important implications: high anti-CCP levels in a person with new-onset joint symptoms predict a more aggressive course with faster erosion and joint destruction.

In clinical practice, anti-CCP titre (level) influences treatment decisions. A very high anti-CCP (more than 3 times the upper limit of normal) is associated with:

• More rapid radiographic progression (joint erosion visible on X-ray)
• Higher likelihood of requiring biologic therapy (such as TNF inhibitors or JAK inhibitors) in addition to standard DMARDs (methotrexate)
• Greater systemic manifestations (rheumatoid nodules, vasculitis)

This is why rheumatologists use anti-CCP not just for diagnosis but as part of risk stratification. It informs how aggressively to treat from the outset and supports the "treat to target" strategy in early RA – aiming for remission or low disease activity to prevent permanent joint damage.