ASCA testing for Crohn's disease:
The anti-Saccharomyces cerevisiae antibody (ASCA) has over recent years been found to be a useful diagnostic marker for Crohn’s disease.
Important points about ASCA testing:
ASCA testing involves determination of the both the IgA and IgG class antibodies. The test is considered abnormal if either or both IgA and IgG antibodies are positive.
The ASCA test is positive in approximately 60-70% of patients with Crohn’s disease, 10-15% of patients with ulcerative colitis and only 0-5% of healthy control subjects. Therefore, the ASCA is particularly useful in helping to differentiate between these two forms of inflammatory bowel disease. Because a significant minority of Crohn’s disease patients do test negative for ASCA, a negative result does not exclude the diagnosis.
Whilst ASCA appears to be reasonably specific for Crohn’s disease, positive results have also been reported in patients with coeliac disease.
Amongst the Crohn’s disease patient population, those testing positive for ASCA appear to have a poorer prognosis than those testing negative. For example, ASCA-positive patients are more likely to develop complications (eg, internal fistulas, fibrostenosis, perianal disease) or require surgical intervention.
As for many other autoimmune disorders, positivity for ASCA may precede clinical disease manifestations by several years.
In the evaluation of patients with suspected inflammatory bowel disease, testing for ASCA is often combined with testing for ANCA. Patients with Crohn’s disease may exhibit the combination of ASCA-positive but ANCA-negative results, whereas those with ulcerative colitis may exhibit the opposing profile of ASCA-negative but ANCA-positive results. When positive in ulcerative colitis, the ANCA usually exhibits the perinuclear (pANCA) pattern.
When to order the ASCA test:
For patients with features of inflammatory bowel disease, to help differentiate Crohn’s disease from ulcerative colitis (order together with ANCA).
For patients with known Crohn’s disease, to help assess risk for disease complications and likely need for surgery.
http://www.moavenandpartners.com/doctors/information_form/asca-testing-for-crohns-disease.shtml