The Anti-CCP test detects antibodies against cyclic citrullinated peptides, which are proteins found in the joints. The presence of these antibodies is highly specific for rheumatoid arthritis (RA) and is used to diagnose and assess the risk of developing RA. It can also help predict the severity of the disease and monitor treatment response. This test is typically used when a patient has symptoms such as joint pain or swelling that suggest rheumatoid arthritis. A blood sample is required for this test.