ASCA and Crohn's disease: what the blood test can tell you

ASCA stands for anti-Saccharomyces cerevisiae antibodies. A laboratory checks a blood sample for these antibodies, which react to components associated with a type of yeast. Some people with Crohn's disease have ASCA in their blood, while others do not. ASCA can also be present without Crohn's disease. A positive result therefore adds context; a negative result does not rule the condition out.

Clinicians interpret the result alongside your symptoms, examination, inflammation markers, stool tests, imaging, and sometimes an examination of the bowel with a camera. Abdominal pain and diarrhoea are common presentations of Crohn's disease, but those symptoms can have many other causes.

Review the report with the clinician who requested it rather than interpreting the word positive or negative alone. Bring a timeline of bowel changes, pain, appetite, weight changes, fever, mouth ulcers, and any blood or mucus in your stool. Mention medicines, recent infections, and close relatives with inflammatory bowel disease because these details can change which tests are useful next.

If Crohn's disease remains a possibility, your clinician may arrange further blood or stool testing or refer you to a gastroenterology specialist. Do not start, stop, or change anti-inflammatory or immune-modifying medicines solely because of an ASCA result.

Arrange prompt medical assessment for ongoing diarrhoea, repeated abdominal pain, unexplained weight loss, fever, or blood in the stool. Seek urgent care for severe or rapidly worsening abdominal pain, a swollen abdomen, persistent vomiting, black or heavy bloody stools, fainting, confusion, or signs of dehydration such as very little urine and marked dizziness. These symptoms need assessment regardless of the ASCA result.

Ask what your ASCA result means alongside your current symptoms and other test results. Useful questions include whether inflammation or infection has been checked, whether a stool test or bowel imaging is appropriate, whether you need a specialist referral, and which changes should prompt urgent care while you wait.