Diseases With Positive Anti-CCP: Beyond Rheumatoid Arthritis

Anti-CCP antibodies are best known as a highly specific marker for rheumatoid arthritis, but a positive result can appear in a surprisingly wide range of other conditions, from lung disease and tuberculosis to lupus and psoriatic arthritis. The test picks up antibodies directed against proteins that have undergone a chemical modification called citrullination, and that modification happens in inflamed tissue regardless of whether the inflammation is joint-related. Understanding which diseases can trigger a positive anti-CCP helps avoid misdiagnosis and gives clinicians a clearer picture of what is actually going on.

What Anti-CCP Antibodies Actually Target

The “CCP” in anti-CCP stands for cyclic citrullinated peptide, a synthetic molecule used in the lab test. The antibodies the test detects are more broadly called anti-citrullinated protein antibodies (ACPAs). They recognize proteins whose arginine amino acids have been converted into citrulline by enzymes called peptidylarginine deiminases (PADs).¹ Citrullination is not inherently abnormal. It happens during cell death, wound healing, and infection. But in rheumatoid arthritis, the immune system treats citrullinated proteins as foreign and mounts a sustained antibody response against them. Those antibodies are found in both blood and joint fluid of RA patients and play an active role in driving joint destruction.²

The reason anti-CCP shows up outside RA is straightforward: any process that ramps up citrullination in inflamed tissue can, in susceptible people, provoke the same type of antibody response. Chronic lung inflammation, certain infections, and other autoimmune diseases all involve tissue damage where citrullination occurs. The test cannot tell you where the antibodies came from or why, only that they are present.

How Specific Is the Test, Really?

Anti-CCP is marketed as highly specific for RA, and depending on the assay used, specificity can be very high. A 2025 comparison of four commercial anti-CCP assays found specificities ranging from roughly 70% to 99%, with sensitivities spanning a similar range.³ That means the best assays will produce a false positive in about 1 in 100 people without RA, but less optimized assays can have a false-positive rate closer to 30%. The particular platform your lab uses matters.

Even with the best assays, “false positive” is a misleading term. In many cases, the antibodies are genuinely present; it is the underlying disease that is not RA. A person with tuberculosis who tests positive is not the victim of a lab error. Their immune system really is producing antibodies against citrullinated proteins. The test result is accurate; the interpretation just has to account for the clinical context.

Lung Disease and the Mucosal Origins Story

Some of the strongest non-RA associations with anti-CCP involve the lungs. Research over the past decade suggests that the lung may even be a primary site where anti-CCP antibodies first develop in people who later go on to get RA. In people who carry anti-CCP antibodies but do not yet have any joint symptoms, investigators have documented local antibody production in lung tissue, along with small-airway disease and increased inflammatory cell activity in sputum.⁴ Sputum from at-risk individuals shows a predominance of the IgA antibody class over IgG, a pattern that flips in established RA, hinting that the lung immune response may be an early stage in the development of the disease.⁵

Beyond this “pre-RA” scenario, outright lung diseases can produce positive anti-CCP results in people who never develop joint disease. A study of patients with anti-CCP antibodies and lung disease but no RA or connective tissue disease identified four patterns on imaging: isolated airways disease in about half, a mix of airways disease and interstitial lung disease in roughly a quarter, isolated interstitial lung disease in a smaller subset, and combined pulmonary fibrosis with emphysema in a handful.⁶ Bronchiectasis patients without RA also show modestly elevated anti-CCP and anti-citrullinated protein responses compared to asthmatics.⁷

COPD is another contributor. A study comparing patients with wood-smoke-induced COPD, tobacco-induced COPD, and healthy controls found that about 14% of the wood-smoke group exceeded the conventional anti-CCP cutoff, compared with 7% in the tobacco group and under 4% in controls.⁸ None of these patients had RA. The common thread is chronic airway inflammation driving citrullination in lung tissue.

Other Autoimmune Diseases

Anti-CCP positivity crops up across the autoimmune disease spectrum. The rates are consistently lower than in RA, but they are not negligible, and in some cases the result carries clinical meaning beyond just a lab curiosity.

Systemic Lupus Erythematosus

Roughly 14–16% of lupus patients test positive for anti-CCP, depending on the cohort studied.⁹ The clinical significance is that anti-CCP-positive lupus patients are far more likely to develop erosive arthritis, a pattern more typical of RA than of lupus. One study found erosive joint disease in about 36% of anti-CCP-positive lupus patients versus only 5% of those who were anti-CCP-negative, and all of the patients with erosive arthritis also met criteria for RA.¹⁰ A meta-analysis confirmed that anti-CCP is a highly specific marker for erosive arthritis in lupus, with pooled specificity above 90%.¹¹ In other words, if you have lupus and your anti-CCP is positive, the chances of destructive joint disease go up substantially, and the overlap condition sometimes called “rhupus” should be on the table.

Psoriatic Arthritis

Anti-CCP positivity in psoriatic arthritis runs between about 7% and 12% across studies.¹²¹³ The pattern that emerges is that anti-CCP-positive psoriatic arthritis patients tend to have polyarticular disease, meaning five or more joints involved. In one study, all five anti-CCP-positive patients had this pattern, compared to a third of anti-CCP-negative patients.¹³ A follow-up study from another group found that anti-CCP-positive psoriatic arthritis patients who were tracked over four years eventually met criteria for RA, even though many also had features typical of psoriatic arthritis such as dactylitis and DIP joint involvement.¹²

The treatment implications are real. Anti-CCP-positive psoriatic arthritis patients had significantly shorter methotrexate survival, meaning the drug stopped working or had to be discontinued sooner. The same pattern held for biologic drugs: anti-CCP-positive patients discontinued their first biologic after a median of about two years, compared to roughly five years in anti-CCP-negative patients, and they were more likely to require multiple biologic switches.¹⁴ Whether these patients truly have an overlap of RA and psoriatic arthritis or a distinct immunological subgroup is still debated, but from a practical standpoint their disease tends to be harder to control.

Sjögren’s Syndrome

About 5–10% of patients with primary Sjögren’s syndrome test positive for anti-CCP, depending on the antibody class measured. One study found moderate-to-high anti-CCP levels in roughly 10% of Sjögren’s patients, and those individuals were about seven times more likely to have synovitis than anti-CCP-negative patients.¹⁵ Interestingly, the synovitis was non-erosive, distinguishing it from the destructive joint disease seen in RA. A separate study looking specifically at IgA-class anti-CCP found positivity in about 8% of Sjögren’s patients, with a notable association with cutaneous vasculitis rather than arthritis.¹⁶

Systemic Sclerosis and Mixed Connective Tissue Disease

Anti-CCP appears in about 9–12% of systemic sclerosis patients and roughly 16% of patients with mixed connective tissue disease (MCTD).¹⁷¹⁸ In systemic sclerosis, the positive results cluster in patients who actually have an overlap with RA, and the antibody levels are significantly higher in that overlap group. In MCTD, anti-CCP-positive patients are more likely to have RA-like and Sjögren’s-like features than those who test negative. Polymyositis and dermatomyositis also show positivity rates around 15%, again predominantly in patients whose disease has overlap features.¹⁸

Infectious Diseases

Infections are an underappreciated source of positive anti-CCP results. A systematic review found that anti-CCP antibodies appeared in various infections at rates reaching 37% in tuberculosis, making TB one of the most frequent non-RA causes of a positive test.¹⁹ TB causes massive tissue necrosis and granuloma formation, both environments where citrullination happens at high levels. In regions where TB is common, this is an important diagnostic consideration when evaluating joint pain alongside a positive anti-CCP.

Hepatitis C is another culprit. Hepatitis C virus (HCV) infection frequently produces rheumatoid factor, which has long been known to muddy the RA diagnostic picture. But anti-CCP antibodies also show up in HCV patients, including those without rheumatoid factor or cryoglobulinemia.²⁰ This matters because HCV commonly causes joint complaints that mimic RA, and the assumption that anti-CCP can reliably separate the two does not always hold.

Leprosy presents a mixed picture. Patients with leprosy had significantly higher serum anti-CCP levels than healthy controls in one study from Mexico.²¹ However, a Brazilian study found actual test positivity (antibody levels above the clinical cutoff) in only about 2.5% of leprosy patients, a modest rate.²² The discrepancy likely reflects differences in how the studies defined positivity and the populations involved, but the takeaway is that leprosy can push anti-CCP levels upward even when no joint disease is present.

The Role of Periodontal Disease

Gum disease has attracted a lot of attention in RA research because the bacterium Porphyromonas gingivalis is one of very few known organisms that produces its own peptidylarginine deiminase, the enzyme that creates citrullinated proteins. The idea is that chronic periodontitis could generate citrullinated antigens in the mouth and kickstart the anti-CCP response. In people who carry anti-CCP antibodies but do not yet have RA, one study found a significantly greater abundance of P. gingivalis at periodontal sites compared to both healthy individuals and patients with established RA.²³

The picture is not clean-cut, though. A study of established RA patients found no significant link between P. gingivalis bacterial load and anti-CCP levels.²⁴ One way to reconcile these findings is that periodontal bacteria may play a role in the initial break of immune tolerance but become less relevant once the autoimmune process is self-sustaining. Whether treating gum disease can prevent or slow RA development in at-risk individuals remains an open question.

Environmental and Occupational Exposures

Inhaling irritants can push the immune system toward producing anti-CCP antibodies, particularly when combined with smoking. Silica exposure, common in mining, construction, and sandblasting, was associated with a moderately increased risk of developing ACPA-positive RA in a Swedish study. Rock drillers had more than double the odds. But the most striking finding was the interaction between silica and smoking: men who were both silica-exposed and current smokers had roughly seven times the risk of developing ACPA-positive RA, an effect greater than what you would expect from adding the two exposures together.²⁵ Neither exposure was linked to ACPA-negative RA, reinforcing the idea that the citrullination pathway specifically is what gets activated by inhaled particulates.

The wood-smoke COPD data described earlier fits this same framework. Repeated inhalation injury to lung tissue, whether from silica, cigarette smoke, or biomass fuel combustion, creates an environment of chronic inflammation and cell death where citrullination flourishes and anti-CCP antibodies can emerge even without any joint involvement.

Anti-CCP Positive Without Any Disease (Yet)

One of the more consequential scenarios is a person whose blood test comes back anti-CCP positive but who has no symptoms of RA or any other identifiable disease. These “at-risk” individuals are increasingly being studied because some of them go on to develop RA and some do not. In a large cohort of over 2,000 people with new musculoskeletal symptoms, about 3% tested positive for anti-CCP. Nearly half of those who were positive developed inflammatory arthritis, most within a year, and the relative risk of developing RA within 12 months was nearly 67-fold compared to those who tested negative.²⁶

The antibody level matters too. A study of clinically tested CCP-positive individuals without RA found that high-level anti-CCP was associated with a 46% chance of progressing to RA within five years, and the hazard was nearly five times that of someone with a low-level positive result, after adjusting for factors like smoking, family history, and rheumatoid factor.²⁷ So a weakly positive test in someone with vague aches is a different story from a strongly positive test, and the distinction has practical value for deciding how aggressively to monitor.

Juvenile Idiopathic Arthritis in Children

Anti-CCP is not commonly ordered in pediatric patients, but it does show up in juvenile idiopathic arthritis (JIA), particularly the polyarticular subtype. One study of 50 JIA patients found anti-CCP positivity in 8%, exclusively in children with polyarticular-onset disease.²⁸ A multicenter trial reported a higher rate of about 24%, again concentrated in polyarticular JIA, and found that anti-CCP positivity correlated with more severe joint damage on X-rays and higher inflammatory markers.²⁹ The children who test positive tend to have a disease course that resembles adult RA more closely than other forms of JIA, and the test may help identify which kids need more aggressive treatment early on.

Cancer and Paraneoplastic Arthritis

Occasionally, joint inflammation triggered by an underlying cancer (paraneoplastic arthritis) can produce a positive anti-CCP result. Case reports have documented anti-CCP-positive polyarthritis as the presenting feature of malignancy, including lung cancer and other solid tumors.³⁰ This is rare, and there are no large cohort studies establishing a reliable prevalence. But it is worth knowing because paraneoplastic arthritis can mimic RA so closely that only the clinical trajectory after cancer treatment (the arthritis resolves) reveals the true cause. A new-onset positive anti-CCP in an older adult with constitutional symptoms like unexplained weight loss or night sweats warrants a broader workup.

Checkpoint Inhibitor Immunotherapy and Anti-CCP

Cancer immunotherapy drugs known as checkpoint inhibitors have become a major cause of new-onset inflammatory arthritis. A natural question is whether these patients develop anti-CCP antibodies the way RA patients do. The answer appears to be no. In a study of 23 patients who were anti-CCP negative before starting checkpoint inhibitor therapy, none became positive during follow-up, even after developing overt inflammatory arthritis, over a median observation period of nearly a year.³¹ This suggests that checkpoint inhibitor arthritis works through a different immune pathway than RA, and it means anti-CCP can help distinguish between the two when joint inflammation appears during cancer treatment.

Making Sense of an Unexpected Positive Result

If you or your doctor are looking at a positive anti-CCP in the absence of classic RA symptoms, a few practical points are worth keeping in mind. First, the antibody level matters. A borderline positive result is far less predictive of RA than a high-level positive, and borderline results are more likely to reflect one of the non-RA conditions discussed here. Second, context is everything. A positive anti-CCP in someone with known lupus or psoriatic arthritis is not a lab error; it likely identifies a subgroup at higher risk for erosive joint disease who may need different management. Third, a positive result in someone with chronic lung disease, active TB, or hepatitis C may be driven entirely by the underlying condition and does not automatically mean RA is developing.

The presence of rheumatoid factor alongside anti-CCP strengthens the case for RA, but rheumatoid factor itself is even less specific and can be triggered by infections, other autoimmune diseases, and aging. When both are present in someone with joint swelling and morning stiffness, RA is the most likely explanation. When anti-CCP is positive but rheumatoid factor is negative and the clinical picture does not fit RA, the differential widens considerably, and the conditions reviewed here should be on the list. Rheumatologists generally weigh the antibody titer, the full clinical presentation, and imaging findings together rather than treating any single test result as diagnostic on its own.