What is being tested?

The anticentromere antibody (ACA) is an autoantibody - a protein produced by the immune system that mistakenly targets the body's own tissues. More specifically, it is one of several antinuclear antibodies and it targets the centromere, a component of the chromosomes found in the nucleus of the body's cells. The Centromere Ab test detects and measures the amount of anticentromere antibody in the blood to help diagnose a form of systemic sclerosis (scleroderma).

Systemic sclerosis is a group of rare connective tissue disorders. There are two distinct subtypes: diffuse cutaneous systemic sclerosis that affects the entire body and limited cutaneous systemic sclerosis. These subsets of systemic sclerosis are defined on the basis of the extent of skin involvement. ACA is found in about 60 - 80 per cent of people who have limited systemic sclerosis. Only about 5 per cent of patients with diffuse systemic sclerosis have ACA.

Limited systemic sclerosis is typically associated with one or more symptoms that were known collectively as CREST syndrome (although this term is no longer in wide medical use). CREST symptoms include:

• Calcinosis – calcium deposits under the skin
• Raynaud phenomenon – episodes of decreased blood flow to fingers and toes, causing them to turn white and blue
• Esophageal dysfunction – difficulty swallowing, acid reflux, and heartburn
• Sclerodactyly – tight, thick, shiny skin on the hands and fingers
• Telangiectasia – red spots on skin due to swollen capillaries

Anticentromere antibody can be present in up to 95 per cent of people who have CREST symptoms.

How is it used?

A Centromere antibody test is primarily ordered to help diagnose systemic sclerosis (scleroderma). The test may be used to distinguish between this and other conditions with similar symptoms.

Testing may be used to provide the doctor with additional information if an ANA (antinuclear antibody) test is positive, especially if the test produces a speckled, nucleolar, or centromere pattern. (For more on this, see "What does the test result mean?" in the ANA article.)

It may be ordered along with SCl-70 (anti-topoisomerase), another autoantibody that may be present with scleroderma.

A Centromere antibody test may be ordered along with other tests for autoantibodies, including ANA.

When is it requested?

An ACA test may be ordered when a person has a positive result on an ANA test and one or more of the CREST symptoms. These symptoms include:

• Calcinosis – calcium deposits under the skin
• Raynaud phenomenon – episodes of decreased blood flow to fingers and toes, causing them to turn white and blue
• Esophageal dysfunction – difficulty swallowing, acid reflux, and heartburn
• Sclerodactyly – tight, thick, shiny skin on the hands and fingers
• Telangiectasia – red spots on skin due to swollen capillaries

What does the result mean?

If a person is positive for ACA and has CREST symptoms, it is likely they have limited systemic sclerosis. ACA is found in about 60 - 80 per cent of people who have limited systemic sclerosis.

If a person is negative for ACA, it is likely that their symptoms are due to another condition. However, it is possible, though rare, that they have limited systemic sclerosis and do not produce anticentromere antibodies.

Is there anything else I should know?

A centromere antibody test can be positive in some other autoimmune disorders, such as systemic lupus erythematosus (lupus), rheumatoid arthritis, or primary biliary cirrhosis.

Typically, only people who have CREST symptoms are tested for ACA. However, some people may be positive for ACA prior to the development of these symptoms and the centromere antibody test may be performed in conjunction with testing for other autoimmune disorders.

The amount of ACA present does not, in general, correlate to the severity of a person's symptoms.

Common questions

• Should everyone have a centromere antibody test?

This test is not intended to be a general screening test. It is typically only indicated when a person has one or more CREST symptoms. Since limited systemic sclerosis is relatively rare, most people will never need to have this test performed.

• Is there anything I can do to decrease my anticentromere antibody level?

In general, no, it does not respond to lifestyle changes.

• Will my anticentromere antibody ever go away?

Concentrations of ACA in the blood may vary over time but once a person has developed ACA, he will continue to produce it.

• Can I perform centromere antibody testing at home?

No. Centromere Ab testing requires specialized equipment and training. It is not offered by every laboratory and will usually need to be sent to a reference laboratory.

More information

RCPA Manual: Centromere antibody

Healthdirect Australia: Scleroderma