ASCA Test - IgG

ASCA IgG test, also known as the anti-Saccharomyces cerevisiae IgG antibody test, helps doctors 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 G (IgG) antibodies in the blood sample. On lab reports, it is often found as ASCA IgG or anti-Saccharomyces cerevisiae IgG antibody.

IBD is a chronic condition that causes inflammation of the digestive tract. Ulcerative colitis most commonly affects the rectum and the large intestine (colon), while Crohn’s disease can affect any part of the gastrointestinal tract.

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

The doctor might advise the ASCA IgG test in individuals with the following symptoms of IBD, to differentiate between Crohn’s disease and ulcerative colitis:

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

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

The ASCA IgG test helps differentiate between the two types of chronic IBD, Crohn’s disease and ulcerative colitis, as part of a diagnostic panel along with the ASCA IgA and pANCA tests.

What to Expect Before the ASCA-IgG Test

No fasting is required for a standalone ASCA-IgG 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-IgG 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-IgG 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 IgG test is:

• Detection of IgG antibodies specific to Saccharomyces cerevisiae associated with IBD.

The following table shows the ASCA IgG test normal range:

Note:

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

The table below provides a general interpretation of ASCA IgGtest results based on whether the levels are positive or negative.

The ASCA IgG test is generally safe and involves minimal risk. Mild pain, bruising, or slight bleeding may occur at the needle site. This usually resolves quickly.

Limitations

Similar to any test, the ASCA IgG test also has some limitations:

• It cannot be used alone in the diagnosis of 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 IgG test results and symptoms, your doctor may recommend the following tests to confirm a diagnosis or identify the underlying cause:

• ASCA IgA test
• pANCA test
• Endoscopy
• Biopsy
• Imaging
• Clinical assessment