Anti-Citrullinated Protein Antibody (ACPA) Test – Serum
Overview:
The Anti-Citrullinated Protein Antibody (ACPA) test, also known as the Anti-CCP (Cyclic Citrullinated Peptide) test, is a blood test used primarily to help diagnose Rheumatoid Arthritis (RA). These antibodies target proteins in the body that have undergone a change (citrullination), which is commonly seen in autoimmune inflammation.

Sample Type:
Serum (blood sample)

A blood sample is drawn, and the serum is tested to detect the presence and level of ACPA/anti-CCP antibodies.

Purpose of the Test:
Aid in the early diagnosis of Rheumatoid Arthritis

Distinguish RA from other types of arthritis or joint diseases

Predict the severity and progression of RA

Support diagnosis when ANA or RF tests are inconclusive

Why Citrullinated Proteins Matter:
Citrullination is a normal process, but in people with RA, the immune system mistakenly recognizes these altered proteins as threats and produces anti-citrullinated antibodies, leading to joint inflammation and damage.

When the Test is Ordered:
Patients with persistent joint pain, swelling, or stiffness

When Rheumatoid Factor (RF) is positive or negative, but RA is still suspected

To confirm RA early, before joint damage occurs

Test Results:
Positive Result: Strongly suggests Rheumatoid Arthritis, especially when symptoms are present

Negative Result: Does not rule out RA, but lowers its likelihood

ACPA is more specific than Rheumatoid Factor (RF) and is often present before symptoms appear

Normal Reference Range:
Negative: <20 U/mL (varies by lab)

Positive: ≥20 U/mL
Higher levels may correlate with more aggressive disease and joint damage.

Advantages of the ACPA Test:
High specificity (~95%) for RA

Helps in early diagnosis and intervention

Can be used to assess prognosis

Limitations:
Not all RA patients test positive

Should be used alongside clinical symptoms, physical exam, and other lab/imaging findings

Conclusion:
The ACPA (Anti-CCP) serum test is a powerful tool in the diagnosis and management of Rheumatoid Arthritis. Its high specificity makes it particularly valuable in distinguishing RA from other joint disorders, especially in the early stages. However, like all autoimmune tests, results must be interpreted in the context of the patient’s clinical presentation.