Anti-Citrullinated Protein Antibody (ACPA) – Serum

What Is This Test Measuring?

ACPA antibodies are proteins produced by your immune system that react against citrullinated proteins—commonly found in joints and blood vessels. These antibodies are strongly associated with rheumatoid arthritis but can also appear in other inflammatory conditions. The test identifies whether your body has produced these antibodies, which may indicate an autoimmune response.

Why Might You Need This Test?

Your healthcare provider may order this test if you have symptoms like joint pain, swelling, or stiffness—common in rheumatoid arthritis. It can also help confirm a diagnosis when other tests are inconclusive or monitor disease progression over time.

How Is the Test Performed?

A blood sample is drawn from a vein in your arm. The serum portion is then tested for ACPA antibodies using an immunoassay method, which detects the presence of these antibodies in your blood.

What Are Common Results and Next Steps?

A positive result suggests an increased likelihood of rheumatoid arthritis or other autoimmune conditions. However, results alone don’t confirm a diagnosis—your provider will consider symptoms, other test results, and clinical findings. Follow-up may include additional blood tests, imaging, or treatment planning.