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
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 due to 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.
The two most common types of IBD are 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, even using biopsies 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.
There are two classes of Saccharomyces cerevisiae antibodies produced by the body, ASCA IgG and ASCA IgA. Testing usually includes both classes. ASCA IgG may predict the severity of the disease and the need for surgery as a treatment option.
How is the test 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.
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. Other antibody tests may also be used in combination with ASCA testing, such as anti-CBir1 (anti-flagellin antibody) and anti-Omp C (anti-outer membrane protein antibody).
When is it ordered?
Signs and symptoms of an IBD may include:
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 with negative test results 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.
Besides ASCA, what other testing may be done?
In some cases, several antibody tests, 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 Anti-CBir1 and anti-Omp C are indicative of CD. The presence of multiple antibodies may indicate the likelihood of a more aggressive disease, but negative results do not rule out aggressive disease.
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.
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. Once a decision has been made, there is generally no need for repeat testing. 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.
Will ASCA go away once they have developed?
How long will it take for my results?
ASCA testing is not offered by every hospital laboratory. It may be necessary to send your blood sample to a reference laboratory for testing and it may take from one day to several days for your results to be available.