The presence of anti-CCP in a person’s blood may indicate they have rheumatoid arthritis (RA). When the immune system produces anti-CCP, it triggers a series of reactions that damage tissues in the joints. This can result in pain, stiffness, and swelling.
Anti-CCP is an auto-antibody. This is a protein the immune system can make that triggers autoimmunity, meaning the immune system begins mistakenly attacking healthy tissues. Doctors may test for anti-CCP if they suspect that a person has RA.
This article discusses anti-CCP testing for RA, including what the test shows, how accurate it is, and what happens if the result is positive or negative.
What is anti-CCP?
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Anti-cyclic citrullinated peptide (CCP) is an auto-antibody. Antibodies are proteins that help with fighting infections. However, auto-antibodies are proteins that cause the immune system to attack healthy tissues.
Anti-CCP invades certain peptides in the lining of joints, causing inflammation. This leads to joint pain, swelling, and, ultimately, joint damage. This is how RA develops, which means people with the condition typically have anti-CCP in their blood.
Generally, doctors combine the results of anti-CCP and rheumatoid factor tests to screen for RA.
Is anti-CCP always positive in RA?
Anti-CCP is not always positive in cases of RA. An older 2016 review by a team of medical experts and rheumatologists found that a positive anti-CCP result depends on how advanced the RA is. Positive anti-CCP results occurred in:
- 23% of people with early stage RA
- 50% of people at the time of their diagnosis
- 53–70% of people 2 years after their diagnosis
This study shows that the timing influences the chances of detecting anti-CCP. Some people with RA may not have a positive anti-CCP test result.
Is anti-CCP specific to RA?
A positive anti-CCP result likely means a person has RA, but it is not specific to RA alone. In a 2020 study, researchers note that it is possible for anti-CCP to be present in people with other diseases, such as tuberculosis, autoimmune hepatitis, and systemic lupus.
Therefore, a positive anti-CCP alone may not confirm RA. Clinical evaluation is also necessary to determine which disease a person has.
Is anti-CCP the same as rheumatoid factor?
Anti-CCP and rheumatoid factor are both auto-antibodies that can help with diagnosing RA. However, they are distinct antibodies.
Rheumatoid factor is the auto-antibody that the immune system produces against connective tissues in the joint. The presence of rheumatoid factor in the blood is not specific to RA but may indicate an autoimmune disease.
A positive rheumatoid factor test combined with a positive anti-CCP test indicates that a person likely has RA.
The anti-CCP test has a 96% specificity, which is highly accurate in determining who does not have anti-CCP. Therefore, experts believe that anti-CCP has more diagnostic accuracy than a rheumatoid factor test.
Typical anti-CCP ranges and results
The typical level of anti-CCP in the blood is less than 20 endotoxin units per milliliter (EU/mL). People with values significantly higher than this reference range may have RA.
If the anti-CCP result is positive, but the rheumatoid factor test is negative, the person may get RA in the future or be in the early stages of the disease.
If both are positive, it is likely that a person has RA or is at risk of developing it. If both are negative, it likely means they do not have RA.
Can an anti-CCP test be wrong?
Anti-CCP test results can occasionally be misleading. For example, there are some other diseases that may cause elevated anti-CCP levels, which could confuse the interpretation of the results.
It is also possible for anti-CCP tests to be negative when a person does have RA. This could happen in the earlier stages of the disease when the test is less likely to be accurate and anti-CCP levels are lower.
The more advanced the RA is, the more likely the test is to be accurate.
What happens next?
If the anti-CCP is positive, a doctor may order a rheumatoid factor test, too. They may also recommend the following investigations:
- X-rays of affected joints
- an erythrocyte sedimentation rate test
- a C-reactive protein test
- antinuclear antibody test
- synovial fluid analysis
The findings of these tests are essential for the accurate diagnosis of RA before a doctor prescribes any treatments.
In contrast, a negative anti-CCP test could mean one of two things. It may mean a person does not have enough anti-CCP in their blood to create a positive result, even though they do have RA. Alternatively, it may mean they do not have RA and that something else is causing their symptoms.
In either case, a doctor will need to order more tests to determine whether the person has RA or whether there is another underlying cause for their joint pain. This may involve medical imaging, blood tests, and other tests.
Summary
Anti-CCP is an auto-antibody. Antibodies are proteins the immune system makes to fight infections, but auto-antibodies trigger autoimmunity, where the immune system attacks a person’s own body.
A positive anti-CCP result typically indicates a person has RA, particularly if they also test positive for rheumatoid factor. Doctors use these two tests to make a diagnosis. They may also perform medical scans of the joints.
If anti-CCP is negative, though, a person may still have RA or be in the early stages of the condition. For this reason, a doctor will typically use several tests and investigations to confirm or rule out RA.
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