Anti-citrullinated protein antibody (ACPA) – Serum

Why This Test Is Done

Doctors may order an ACPA test if you have symptoms like joint pain, swelling, or stiffness—especially if these symptoms occur in the same joints on both sides of your body. It’s often used alongside other tests, such as rheumatoid factor (RF), to help confirm a diagnosis of rheumatoid arthritis or monitor disease progression.

What to Expect Before the Test

No special preparation is needed. You’ll have a small needle inserted into your arm to draw blood. The process usually takes a few minutes, and you may feel a brief pinch. If you’re on blood thinners or have a history of bleeding, let your doctor know beforehand.

What the Results Mean

ACPA levels can be positive in people with rheumatoid arthritis, but they’re also found in some healthy individuals. A positive result suggests a higher likelihood of the disease, but it’s not definitive on its own. Your doctor will consider the result alongside other factors, like symptoms, physical exam, and imaging studies.

Common Misconceptions About ACPA

ACPA testing isn’t a definitive cure or treatment for rheumatoid arthritis. It’s a diagnostic tool to help identify the condition and guide treatment decisions, such as medications to reduce inflammation.