Anti-CCP test: what a positive result means for RA

Anti-CCP antibodies are antibodies your immune system makes against proteins that carry citrulline, and they are the most specific blood test for rheumatoid arthritis (RA). In a meta-analysis of 37 studies, anti-CCP was positive in about 2 of every 3 people with RA and in only about 5 of every 100 people without it.¹ It can also turn positive years before the joints swell, which makes it an early warning as well as a diagnostic clue.²

The short version

• Normal: negative, which on many U.S. tests means under 20 units. Each test sets its own line, from 3 to 25 units, so check the range on your report.³⁴⁵
• Positive: points strongly to RA, especially next to a positive rheumatoid factor (RF). The higher the level, the stronger the signal: more than 3 times your lab's cutoff counts as "high-positive" in the RA classification criteria.¹⁶⁷
• Early warning: about half of people who later got RA had anti-CCP or RF in stored blood a median of 4.5 years before symptoms. Among 100 people with joint aches and a positive anti-CCP, half developed arthritis, most of them within a year.²⁸
• Urgent: new swelling in the small joints of the hands or feet, or in more than one joint, needs prompt care whatever your anti-CCP shows.⁹

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What anti-CCP is

Your body makes small chemical changes to some of its own proteins after they're built. One of them is citrullination: enzymes called PADs turn the amino acid arginine into a close cousin, citrulline.¹⁰¹¹ In some people the immune system starts treating these citrullinated proteins as foreign and makes antibodies against them, called anti-citrullinated protein antibodies (ACPA).¹²

The lab test catches those antibodies with a man-made, ring-shaped ("cyclic") citrullinated peptide, which is where the name anti-CCP comes from. The second-generation peptides (CCP2) are the most widely used, and some tests also count IgA antibodies alongside the usual IgG.¹³³

Anti-CCP is usually ordered when someone has joint pain, stiffness or swelling, often together with or after an RF test.⁶ Of the two, anti-CCP is the more specific. The Nishimura meta-analysis found anti-CCP positive in 67% of people with RA and negative in 95% of people without it, versus 69% and 85% for IgM RF.¹

What's a normal anti-CCP?

Negative is normal. On many U.S. tests that means under 20 units: ARUP, a commercial reference lab, reports 19 units or less as negative, and the Hospital for Special Surgery (HSS) uses under 20.³⁴

The line moves with the test, though. When researchers ran nine commercial anti-CCP tests on the same 1,471 blood samples, the manufacturers' positive lines ranged from 3 to 25 units. At those lines, each test caught 58–65% of RA and read negative in 95–98% of people without it.⁵ So read your number against the range printed on your own report.

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A positive result in the general population is uncommon. In the Dutch Lifelines study of 40,136 adults, 1.0% tested positive, and 0.8% of those without RA. Positives were more common with older age, in women, in smokers and in people with joint complaints.¹⁴ Labs use one cutoff for men and women.³

"Optimal" anti-CCP: what health optimizers aim for

For most markers, optimizers aim for a tighter band inside the lab range. Anti-CCP works differently: it's an antibody most healthy people lack, so "optimal" simply means as low as the test reads. Here's the ladder, from strictest to loosest:

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Why the level matters, even near "negative":

• Across nine tests, results near the manufacturers' cutoffs barely changed the odds of RA. A result in the next band up was 7–13 times more likely in RA than in patients without it, and one in the top band 80–107 times.⁵
• Among 640 people with early inflammatory arthritis, a higher starting anti-CCP predicted more joint damage on X-rays 5 years later, even below the positive line: levels of 2–5 U/ml carried 3.6 times the odds of erosions.¹⁵
• Among 100 people with new joint aches and a positive anti-CCP, half developed arthritis over a median follow-up of about 20 months. A high-positive antibody result was one of four warning signs in the study's risk score. With a score of 3 or more, 62% developed arthritis, versus none of the five people who scored 0.⁸

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Keep "optimal" in perspective: a negative anti-CCP is reassuring, not a clean bill of joint health. About 1 in 5 people with RA have neither anti-CCP nor RF, and their diagnosis rests on the exam and imaging.⁴ Anti-CCP also behaves differently from cholesterol or blood sugar: once positive, it usually stays positive, even when RA goes into remission.⁴

What a positive anti-CCP usually means

The level is the first clue. Many labs grade a positive result, and the RA classification criteria split positives at 3 times the lab's cutoff.³⁷

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The usual reasons, most common first

• Rheumatoid arthritis. In people tested for joint symptoms, this is the main reason for a positive result: a positive anti-CCP raises the odds of RA about 12-fold.¹ MedlinePlus puts it plainly: with symptoms, a positive anti-CCP plus a positive RF means you probably have RA.⁶
• RA on the way. Anti-CCP can show up years before the joints swell. In blood-bank samples from people who later developed RA, it was positive in 25% of samples taken more than 18 months before symptoms and in 52% of those taken closer to onset.¹⁶ Among people with joint aches and a positive anti-CCP, about half developed arthritis in one study, most of them within a year.⁸ In another, 26 of the 29 people with joint pain who went on to arthritis were anti-CCP positive, and anti-CCP, rather than RF, predicted who would.¹⁷
• A positive without RA. About 1 in 125 adults without RA test positive (0.8% in the Dutch study), more often older people, smokers and people with joint complaints.¹⁴ People can carry these antibodies for long periods without developing disease.¹²
• Less common: other autoimmune diseases such as Sjögren's syndrome or lupus, active tuberculosis, and chronic lung disease.⁶

Seropositive vs seronegative RA

Rheumatologists split RA by these antibodies. Seropositive RA means a positive anti-CCP or RF. Seronegative means both are negative, which is the case for about 1 in 5 people with RA.⁴

The split matters because the two behave differently:

• Different roots. In a case-control study of recent-onset RA, smoking and certain immune genes (the HLA-DR "shared epitope") were tied to anti-CCP-positive RA and not to the antibody-negative kind. Smokers carrying two copies of those genes had 21 times the RA risk of nonsmokers with none.¹⁸
• A harder course. In 279 people with early RA, those who were anti-CCP positive had more active disease and more joint damage on X-rays over 5 years, despite at least as much treatment.¹⁹ Three of four studies in the Nishimura meta-analysis found faster X-ray damage with anti-CCP than with RF.¹
• A stricter target. The UK's NICE guideline tells people with a positive anti-CCP that their risk of joint damage on X-rays is higher, and suggests considering full remission as the treatment goal.⁹

Get prompt care if you have new swelling in the small joints of your hands or feet, swelling in more than one joint, or joint symptoms that went 3 months or more before you got them checked. NICE calls for an urgent specialist referral in these cases, even when anti-CCP, RF and inflammation tests are normal.⁹ Morning stiffness, tiredness and a low-grade fever often travel with RA.⁶

Anti-CCP reads best next to its neighbors

Anti-CCP rarely comes alone. RF, the inflammation tests CRP and ESR, and often an ANA come with it, and the pattern says more than any one number.⁶

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CRP and ESR show how inflamed things are right now, so doctors repeat them to follow treatment. Anti-CCP answers a different question, what kind of arthritis it is, so it's usually measured once.⁴

How fast anti-CCP changes

It comes early and stays. In one study of blood donors, RF or anti-CCP turned up a median of 4.5 years before RA symptoms began, and up to 13.8 years before.² In another, the share of future RA patients testing positive for anti-CCP climbed from 25% to 52% as onset approached.¹⁶

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What that means in practice:

• Once positive, usually always positive. Over 5 years of early RA, only 3.9% of people changed anti-CCP status, even though levels fell in the first year of treatment.¹⁹ In a group of 640 people, 2% turned positive and 4.6% of positives turned negative, while RF status changed in 17%.¹⁵
• After diagnosis, repeat tests add little. Rechecking anti-CCP after 5 years predicted joint damage no better than the first result (75% vs 74% accuracy).¹⁵ Changes in the level also fail to track how active the arthritis is.¹⁹
• A weak positive is the exception. Labs suggest repeating a result in the 20–39 range, because results near the line shift the odds the least.³⁵

Going deeper: citrulline, smoking and genes

Citrullination is done by a family of five PAD enzymes (peptidylarginine deiminases). PAD2 and PAD4 are the ones most tied to RA.¹¹ Citrulline is an arginine that has been chemically changed after the protein was built, and the antibodies against citrulline-containing peptides are what mark RA: the first research tests found them in 76% of RA blood samples, with 96% specificity.¹⁰

The leading theory starts outside the joints. Smoking raises PAD activity in the airways, and smokers' lung cells carry citrullinated proteins that nonsmokers' cells lack.¹²¹⁸ In people with the shared-epitope genes, that may be enough to set off the antibody response,¹⁸ years before arthritis appears.² People who are antibody positive can already have joint pain and bone loss before RA is diagnosed.¹²

The test itself has changed. The first commercial test used a peptide from the skin protein filaggrin, folded into a ring so antibodies could grip it. The second-generation CCP2 peptides came from screening about 12 million candidates against RA blood.¹³ Because each company sets its own scale and cutoff, the same blood can give quite different numbers on different tests.⁵¹³

Questions worth asking

• Is my anti-CCP negative, weak or strongly positive on this lab's scale, and how far above the cutoff is it?
• What did my RF, CRP and ESR show at the same time?
• Do I have swelling you can see or feel, or only aches? Would an ultrasound help?
• If I'm positive without arthritis, how often should my joints be checked, and which symptoms should bring me back sooner?
• Does smoking change my risk, and what would quitting do?
• If I have RA, does my antibody status change the treatment target?

FAQ

What is a normal anti-CCP level? Negative. On many U.S. tests that means under 20 units, but each test sets its own cutoff, so use the range on your report.³⁴⁵

Does a positive anti-CCP mean I have rheumatoid arthritis? It makes RA much more likely, especially with joint symptoms and a positive RF. Some people test positive years before RA starts, and about 0.8% of adults without RA test positive.¹⁶¹⁴

Can anti-CCP be positive before symptoms? Yes. In stored blood, RF or anti-CCP appeared a median of 4.5 years before RA symptoms. In one study, half of people with joint aches and a positive anti-CCP developed arthritis.²⁸

Can a negative anti-CCP rule out RA? No. About a third of people with RA test negative, and about 1 in 5 have neither anti-CCP nor RF. If your joints are swollen, see a clinician whatever the result.¹⁴⁹

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This guide is for education. It can't diagnose you or replace care from a clinician who knows your history.

Footnotes

1. Nishimura K, Sugiyama D, Kogata Y, et al. Meta-analysis: diagnostic accuracy of anti-cyclic citrullinated peptide antibody and rheumatoid factor for rheumatoid arthritis. Ann Intern Med. 2007;146(11):797–808. Pooled 37 anti-CCP and 50 RF studies: anti-CCP sensitivity 67%, specificity 95%, positive likelihood ratio 12.46; IgM RF 69% and 85%. PubMed ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹

2. Nielen MM, van Schaardenburg D, Reesink HW, et al. Specific autoantibodies precede the symptoms of rheumatoid arthritis: a study of serial measurements in blood donors. Arthritis Rheum. 2004;50(2):380–386. 79 future RA patients: 49% positive for IgM RF and/or anti-CCP a median 4.5 years (range 0.1–13.8) before symptoms; 0.6% of 2,138 control samples anti-CCP positive. PubMed ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶

3. ARUP Laboratories. Cyclic Citrullinated Peptide Antibody, IgG and IgA (test 3016632). Reference interval 19 units or less; 20–39 weak positive, 40–59 moderate, 60 or more strong; weak positives should be monitored and repeated. A commercial reference lab, cited for its published cutoffs. ARUP ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰ ↩¹¹ ↩¹²

4. Richey M. Understanding Rheumatoid Arthritis Blood Test Results. Hospital for Special Surgery; updated September 9, 2020. Anti-CCP under 20 units is normal; about 20% of RA is seronegative; anti-CCP usually stays positive in remission; ESR and CRP track disease activity. HSS ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰ ↩¹¹ ↩¹² ↩¹³

5. Van Hoovels L, Vander Cruyssen B, Sieghart D, et al. Multicentre study to improve clinical interpretation of rheumatoid factor and anti-citrullinated protein/peptide antibodies test results. RMD Open. 2022;8(1):e002099. Nine anti-CCP tests run on 398 RA and 1,073 control samples; manufacturer cutoffs, sensitivity, specificity and level-specific likelihood ratios. PMC ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰

6. National Library of Medicine. CCP Antibody Test. MedlinePlus. Updated June 3, 2024. How to read anti-CCP with RF, symptoms that prompt the test, and other conditions that can cause a positive result. MedlinePlus ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰ ↩¹¹

7. Aletaha D, Neogi T, Silman AJ, et al. 2010 Rheumatoid arthritis classification criteria: an American College of Rheumatology/European League Against Rheumatism collaborative initiative. Arthritis Rheum. 2010;62(9):2569–2581. The current RA classification criteria. They define low-positive serology (above the lab's upper limit, up to 3 times it) and high-positive (more than 3 times). PubMed · ACR criteria page ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶

8. Rakieh C, Nam JL, Hunt L, et al. Predicting the development of clinical arthritis in anti-CCP positive individuals with non-specific musculoskeletal symptoms: a prospective observational cohort study. Ann Rheum Dis. 2015;74(9):1659–1666. 100 people followed a median 19.8 months; 50 developed arthritis (median 7.9 months), 34 within 12 months. PubMed ↩ ↩² ↩³ ↩⁴ ↩⁵

9. National Institute for Health and Care Excellence. Rheumatoid arthritis in adults: management (NICE guideline NG100). Published 2018. Recommendations 1.1.1–1.1.6 and 1.2.2 on referral, anti-CCP testing and treatment targets. NICE ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶

10. Schellekens GA, de Jong BA, van den Hoogen FH, van de Putte LB, van Venrooij WJ. Citrulline is an essential constituent of antigenic determinants recognized by rheumatoid arthritis-specific autoantibodies. J Clin Invest. 1998;101(1):273–281. PMC ↩ ↩²

11. Curran AM, Naik P, Giles JT, Darrah E. PAD enzymes in rheumatoid arthritis: pathogenic effectors and autoimmune targets. Nat Rev Rheumatol. 2020;16(6):301–315. PubMed ↩ ↩²

12. Catrina A, Krishnamurthy A, Rethi B. Current view on the pathogenic role of anti-citrullinated protein antibodies in rheumatoid arthritis. RMD Open. 2021;7(1):e001228. PMC ↩ ↩² ↩³ ↩⁴

13. Rönnelid J, Turesson C, Kastbom A. Autoantibodies in rheumatoid arthritis: laboratory and clinical perspectives. Front Immunol. 2021;12:685312. History of the CCP tests; ANA positive in 20–38% of people with RA. PMC ↩ ↩² ↩³ ↩⁴

14. van Zanten A, Arends S, Roozendaal C, et al. Presence of anticitrullinated protein antibodies in a large population-based cohort from the Netherlands. Ann Rheum Dis. 2017;76(7):1184–1190. 40,136 Lifelines participants: 1.0% positive, 0.8% of those without RA. PMC ↩ ↩² ↩³

15. Burr ML, Viatte S, Bukhari M, et al. Long-term stability of anti-cyclic citrullinated peptide antibody status in patients with early inflammatory polyarthritis. Arthritis Res Ther. 2012;14(3):R109. 640 people from the Norfolk Arthritis Register tested at baseline and 5 years, with a 5 U/ml positive line. PMC ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶

16. Rantapää-Dahlqvist S, de Jong BA, Berglin E, et al. Antibodies against cyclic citrullinated peptide and IgA rheumatoid factor predict the development of rheumatoid arthritis. Arthritis Rheum. 2003;48(10):2741–2749. 83 people who gave blood before RA began: anti-CCP in 33.7% of pre-onset samples (IgM RF 19.3%); 25% more than 1.5 years before symptoms and 52% within 1.5 years. PubMed ↩ ↩² ↩³ ↩⁴ ↩⁵

17. Bos WH, Wolbink GJ, Boers M, et al. Arthritis development in patients with arthralgia is strongly associated with anti-citrullinated protein antibody status: a prospective cohort study. Ann Rheum Dis. 2010;69(3):490–494. 147 people with joint pain; 26 of 29 who developed arthritis were ACPA positive; ACPA, not IgM RF, predicted arthritis. PubMed ↩

18. Klareskog L, Stolt P, Lundberg K, et al. A new model for an etiology of rheumatoid arthritis: smoking may trigger HLA-DR (shared epitope)-restricted immune reactions to autoantigens modified by citrullination. Arthritis Rheum. 2006;54(1):38–46. Case-control study of recent-onset RA with lung-cell staining. PubMed ↩ ↩² ↩³

19. Rönnelid J, Wick MC, Lampa J, et al. Longitudinal analysis of citrullinated protein/peptide antibodies (anti-CP) during 5 year follow up in early rheumatoid arthritis: anti-CP status predicts worse disease activity and greater radiological progression. Ann Rheum Dis. 2005;64(12):1744–1749. 279 people with early RA; 3.9% changed status over 5 years. PMC ↩ ↩² ↩³ ↩⁴

20. Nielen MM, van Schaardenburg D, Reesink HW, et al. Increased levels of C-reactive protein in serum from blood donors before the onset of rheumatoid arthritis. Arthritis Rheum. 2004;50(8):2423–2427. CRP was slightly higher before RA onset than in matched controls. PubMed ↩

21. Ingegnoli F, Castelli R, Gualtierotti R. Rheumatoid factors: clinical applications. Dis Markers. 2013;35(6):727–734. RF frequency by condition (Table 1). PMC ↩ ↩²

22. National Library of Medicine. ANA (Antinuclear Antibody) Test. MedlinePlus. Updated March 19, 2025. A positive ANA may be a sign of lupus or another autoimmune disease. MedlinePlus ↩