Anti-Saccharomyces cerevisiae Antibodies (ASCA)
When you have symptoms such as persistent or intermittent diarrhea and abdominal pain that your healthcare practitioner suspects may be due to an IBD; when your healthcare practitioner wants to distinguish between CD and UC
A blood sample drawn from a vein in your arm
Anti-Saccharomyces cerevisiae antibodies (ASCA) are immune proteins that are frequently present in people who have inflammatory bowel disease (IBD). This test detects ASCA in the blood.
S. cerevisiae are common yeast found in various foods. The correlation between the presence of antibodies to S. cerevisiae and their involvement in the inflammatory bowel disease process is not understood at this time.
IBD is a group of chronic disorders, thought to be an autoimmune process, characterized by swollen and damaged tissues in the lining of the intestinal tract. The symptoms and severity of IBD vary from person to person and may fluctuate over time. Many of those affected experience flare-ups followed by periods of lessened symptoms or even remission.
Testing for ASCA can be useful in helping to distinguish between the two most common types of IBD, Crohn disease (CD) and ulcerative colitis (UC). CD can affect any part of the intestinal tract, from mouth to anus, but is primarily found in the small intestine and/or in the colon, while UC occurs in the colon.
The diagnosis of CD or UC is usually made on the basis of endoscopic testing and the examination of biopsy samples from the intestines. Because both CD and UC can be found in the colon, it can sometimes be difficult to distinguish between the two. When this occurs, ASCA testing may be helpful as ASCA is much more frequently found in people with CD than in those with UC.
Sometimes several antibodies, including ASCA, perinuclear anti-neutrophil cytoplasmic antibody (pANCA), anti-CBir1 (anti-flagellin antibody), and anti-Omp C (anti-outer membrane protein antibody), may be ordered together as a panel and the overall findings evaluated to either help distinguish between CD and UC or to try to help determine a prognosis for a person's CD. The presence of multiple antibodies may indicate the likelihood of a more aggressive disease, but negative results do not rule out aggressive disease.
How is the sample collected for testing?
A blood sample is obtained by inserting a needle into a vein in the arm.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.
How is it used?
The test for anti-Saccharomyces cerevisiae antibodies (ASCA) is used to help distinguish between Crohn disease (CD) and ulcerative colitis (UC), the two most common types of inflammatory bowel disease (IBD). Testing usually includes detecting two different classes of ASCA in the blood, IgG and IgA.
ASCA are immune proteins that are frequently present in people who have IBD. The association between the presence of ASCA and their involvement in the disease process, however, is not understood at this time.
IBDs are primarily diagnosed through non-laboratory evaluations, such as a biopsy of the intestine. In some cases, however, it can be difficult to distinguish between CD and UC. An ASCA test is often ordered along with a test for perinuclear anti-neutrophil cytoplasmic antibody (pANCA) to help determine which type of IBD a person has. The presence of ASCA is more common in CD, while pANCA is more common in UC. Anti-CBir1 (anti-flagellin antibody) and anti-Omp C (anti-outer membrane protein antibody) are indicative of CD and may also be used in combination with ASCA testing.
Since the symptoms associated with IBD may be seen with a number of conditions, other tests are frequently performed prior to or along with ASCA testing to rule out other causes for the symptoms. For more on this, see the article on Inflammatory Bowel Disease.
When is it ordered?
ASCA testing is primarily ordered when a person has signs and symptoms that suggest IBD and a healthcare practitioner is attempting to distinguish between CD and UC. It may be ordered along with pANCA and other antibody testing.
Signs and symptoms of an IBD may include:
- Abdominal pain and cramps
- Rectal bleeding
- In some people, joint, skin, bone and organ-related symptoms
- Children may also have delayed development and growth retardation.
What does the test result mean?
A positive ASCA result is not diagnostic of CD, UC, or of an IBD, but it does make it more likely that a person with symptoms has an IBD.
Results of ASCA testing are often interpreted in conjunction with the results of pANCA testing:
- If ASCA is positive and pANCA is negative, then it is likely that the person has CD.
- If ASCA is negative and pANCA is positive, then it is likely that the person has UC.
A negative result for ASCA and pANCA does necessarily rule out IBD. A person who is negative may still have CD, UC, or another IBD.
The presence of multiple antibodies (ASCA, anti-CBir1, anti-Omp C) may indicate the likelihood of a more aggressive disease, but negative results do not rule out aggressive disease.
Is there anything else I should know?
Is it necessary to perform ASCA testing more than once?
Testing is usually only performed once, to help distinguish between CD and UC. It is typical to order tests for the two classes of antibody, ASCA IgG and ASCA IgA, at the same time. However, if only one of the types was initially ordered, then the other type (or more likely both) may be ordered at a later date.
Should everyone with abdominal pain and diarrhea have this test performed?
Will ASCA go away once they have developed?
The level of antibody may vary over time, but once a person's body has produced ASCA, it will continue to be present.
Can ASCA testing be performed in my doctor's office?
On This Site
Elsewhere On The Web
Crohn's and Colitis Foundation of America: Diagnosing and Managing IBD
National Digestive Diseases Information Clearinghouse: Crohn's Disease
National Digestive Diseases Information Clearinghouse: Ulcerative Colitis
MedlinePlus Medical Encyclopedia: Crohn's disease
Mayo Clinic: Inflammatory bowel disease