The anti-cyclic citrullinated peptides (CCP) test is an extremely specific blood test for rheumatoid arthritis (RA) diagnosis. It is also used to predict the likelihood that RA will develop, even before symptoms of this form of arthritis have been observed. Diagnosis of RA is typically based on symptoms consistent with this form of arthritis and the results of the blood tests for anti-CCP and rheumatoid factor, another less specific blood marker for RA.
RA is a autoimmune disease during which the body’s immune system becomes confounded and begins to inwardly attack the body. One of the primary symptoms of RA is swollen and painful joints. Inflammation in the body produces arginine, an amino acid part, that is sometimes converted into a different amino acid called citrulline. People with RA produce antibodies against chains of these citrullin amino acids called anti-cyclic citrullinated peptide antibodies. The anti-CCP blood test detects the presence of these antibodies.
This test is valuable for many reasons. First, the anti-CCP test can confirm a diagnosis when symptoms of RA are present. Second is its ability to detect anti-cyclic citrullinated peptide antibodies in the blood of people before symptoms have developed. Third, the presence of high concentrations of anti-cyclic citrullinated peptide antibodies in the blood, before symptoms appear, strongly suggests a more aggressive form of RA. This kind of information can allow treatment to begin early on, perhaps staving off joint damage, and help rheumatologists determine how strongly to treat the disease.
Prior to the development of the anti-CCP test, diagnosis of RA depended heavily on a blood test for rheumatoid factor (RF). This test is sometimes negative in people with RA and sometimes positive in people who do not have RA or never develop this form of arthritis. Diagnosis of RA is now typically based on the symptoms, as well as the results of the blood tests for RF and anti-CCP.
If symptoms of RA are observed and the RF and anti-CCP blood tests are both positive, a diagnosis of RA is made. When a patient has a positive RF and a negative anti-CCP test, the doctor will typically order further tests and make a determination based on the results of those test as well as the symptoms and their severity. If the anti-CCP test is positive, the RF test is negative, and symptoms are present, the diagnosis is for RA. When the anti-CCP test is positive, the RF test is negative, and no symptoms are present, the assumption is that RA has a strong likelihood of developing in the future. If both blood tests are negative but symptoms of RA are present, then an alternative reason for the symptoms may be sought and the diagnosis of RA may be delayed or abandoned.