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Serum or Plasma Substance Concentration (Mass) – Anti-Citrullinated Protein Antibodies (ACPA)

Published: August 9, 2026Updated: August 16, 2026

This test measures the presence of antibodies against citrullinated proteins in your blood. These antibodies are often linked to rheumatoid arthritis.

Quick summary

["ACPA antibodies may help diagnose or monitor rheumatoid arthritis."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
39590-5
Short code
HTLV I+II p19 Ab Ser-aCnc
Synonyms
HTLV I+II p19 Ab Ser-aCnc
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Specimen volume
5 mL
Stability
Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
500
Lipemia max
1000
Icterus max
500
TAT
4–24 hours
Order
routine

Why This Test Might Be Ordered

Your healthcare provider may recommend this test if you have symptoms of rheumatoid arthritis, such as joint pain, swelling, or stiffness, especially if they occur in the same joints on both sides of your body. It may also be used to assess disease activity or response to treatment in people already diagnosed with rheumatoid arthritis.

What to Expect Before the Test

No special preparation is usually needed. You may be asked to fast before the test, but this is often not required for antibody tests. Bring any medications you’re currently taking, as some may affect results.

What the Test Involves

A healthcare professional will draw blood from a vein in your arm using a small needle. You may feel a brief pinch, but it’s usually over quickly. The blood sample is then sent to a lab for analysis.

What the Results Mean

Results are qualitative (positive or negative) and indicate whether ACPA antibodies are present. High levels may suggest an increased risk of rheumatoid arthritis or disease activity in the condition. Results alone do not diagnose rheumatoid arthritis; they are used alongside other tests and clinical findings.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

ACPA antibodies are a specific marker for rheumatoid arthritis, particularly in people who test positive for rheumatoid factor. They can help confirm the diagnosis, assess disease severity, and guide treatment decisions. While not all people with rheumatoid arthritis have ACPA antibodies, they are more common in those with early or active disease.

Short name

ACPA Antibody Test

Frequently asked questions

What does a positive result mean?
A positive result means your blood contains antibodies against citrullinated proteins, which may indicate an increased risk of rheumatoid arthritis or an active inflammatory condition. This finding should be discussed with your healthcare provider to determine next steps, such as further testing or treatment planning.
Can this test be used to diagnose rheumatoid arthritis?
No, this test alone cannot diagnose rheumatoid arthritis. It is one piece of the puzzle. Your healthcare provider will use the test results along with your symptoms, physical exam, and possibly other tests (like rheumatoid factor or imaging) to make a diagnosis.
How often should I get this test?
Your healthcare provider will determine how often you need this test based on your individual health needs. It may be part of routine monitoring if you have rheumatoid arthritis or another related condition, or it may be done less frequently if you are asymptomatic or under observation for early disease.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.

This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.

Medical Disclaimer

This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.

If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.

Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy