ASCA Test - IgA

The ASCA IgA test, also known as the anti-Saccharomyces cerevisiae IgA antibody test, helps the doctor to differentiate between two types of inflammatory bowel disease (IBD) involving the gastrointestinal tract: ulcerative colitis and Crohn's disease. The test checks for the presence of ASCA immunoglobulin A (IgA) antibodies in the blood sample. On lab reports, it is often found as ASCA IgA or anti-Saccharomyces cerevisiae IgA antibody.

IBD is a group of long-term conditions that cause inflammation of the digestive tract. Ulcerative colitis most commonly affects the rectum and large intestine (colon), while Crohn's disease can affect any part of the gastrointestinal tract.

IgA antibodies against the yeast Saccharomyces cerevisiae are often found in IBD. For an accurate diagnosis, this test is usually done together with the ASCA IgG and pANCA (perinuclear anti-neutrophil cytoplasmic antibody) tests to support the diagnosis. High levels of ASCA IgG and IgA are found in Crohn's disease, while positive pANCA tests are common in ulcerative colitis.

The doctor might advise the ASCA IgA test in individuals with symptoms of IBD to help differentiate between Crohn's disease and ulcerative colitis, such as:

• Long-term diarrhoea
• Abdominal discomfort and pain
• Unexplained tiredness
• Loss of weight
• Blood in the stool

The ASCA IgA test is usually performed once, as advised by the doctor, when IBD symptoms are observed.

The ASCA IgA test helps in differentiating between the two types of IBD, Crohn's disease and ulcerative colitis, along with the ASCA IgG and pANCA tests.

What to Expect Before the ASCA-IgA Test

No fasting is required for a standalone ASCA-IgA test. You can eat and drink normally. However, if it is part of a broader package that includes fasting tests, your doctor may advise fasting for 8-12 hours. Avoid strenuous exercise for 24 hours before the test, as intense physical activity can temporarily raise ASCA-IgA levels and affect interpretation. Always inform your doctor about any ongoing medications.

What to Expect During the Blood Collection

A phlebotomist cleans the skin with an antiseptic, then places an elastic band around your upper arm to make the veins easier to access. A small needle is inserted into the vein; you may feel a brief pinch. Blood is collected into a labelled tube in under a minute.

What to Expect After the ASCA-IgA Test

A small cotton swab and bandage are placed over the site to stop any minor bleeding. You can return to normal activities immediately. Minor bruising is normal and disappears quickly. If dizzy, sit and rest for a few minutes.

The key parameter in the ASCA IgA test is:

• Detection of IgA antibodies specific to Saccharomyces cerevisiae involved in IBD.

The following table shows the ASCA IgA test normal range:

Note:

• Normal ASCA IgA levels can vary based on age, sex, and the laboratory method used.
• Medical history and symptoms are to be considered along with the test results by the doctor.

The table below provides a general interpretation of ASCA IgA test results, depending on whether the levels are positive or negative. 

The ASCA IgA test is generally safe and has very little risk. Mild pain, bruising, or slight bleeding may occur at the needle site. This usually resolves soon.

Limitations

Similar to any other test, the ASCA IgA test may also have some limitations:

• It cannot be used alone to diagnose ulcerative colitis or Crohn's disease.
• Other follow-up tests must be done to confirm the diagnosis.
• A negative result cannot completely rule out Crohn's disease.
• Positive results should be evaluated along with other tests and clinical findings.

Depending on your ASCA IgA test results and symptoms, your doctor may recommend additional tests, such as the following, to confirm a diagnosis or identify the underlying cause:

• ASCA IgG test
• ANCA test
• Endoscopy
• Biopsy
• Imaging
• Clinical assessment