What is the ASCA/ANCA test?
Various markers in the blood can assist in diagnosing inflammatory bowel diseases. The two most common tests found in most healthcare systems are ANCA, primarily relevant to ulcerative colitis, and ASCA, primarily relevant to Crohn's disease. These serological tests essentially detect antibodies (ANCA against cellular components and ASCA against bacterial components) that, as of today's knowledge, aren't crucial in the development of inflammation. Instead, they only indicate the presence of the disease. There are other serological systems worldwide (Prometheus in the US and Glycomyde in Israel), but these are not available within the framework of health fund systems, and their high cost generally does not justify frequent use except in specific cases.
When is it advisable to be tested using this method?
Blood tests can be conducted at the time of diagnosis for three purposes: First, similar to the Calprotectin test, to identify patients with complaints of irritable bowel symptoms who need further clarification (such as colonoscopy, imaging, or Calprotectin in stool) for suspected inflammatory bowel diseases. Second, to differentiate between ulcerative colitis and Crohn's disease in cases of atypical inflammation in the colon, which could fit both ulcerative colitis and Crohn's disease (referred to as IBD-Unclassified or IBD-U). Third, to predict the course of the disease. In various studies, positive serological tests in the blood have been found to indicate a more severe disease course with an increased risk of surgeries and hospitalizations. However, it's important to emphasize that beyond the research-academic aspect, it's not common practice to send serology for this purpose alone, as we can't accurately assess the risk and translate it into practice for treatment.
Is the test reliable?
Not particularly, but a positive result might assist in diagnosis. The positive rate of ASCA (with negative ANCA) in the presence of Crohn's disease is around 70%, while the positive rate in the general population is about 5%. A positive ANCA in ulcerative colitis (with negative ASCA) is about 60%-70%, while its rate in the general population is 10%-15%. The accuracy decreases when dealing with inflammation in the colon of the IBD-U type, aimed at distinguishing between ulcerative colitis and Crohn's disease. The higher the obtained result, the higher the reliability of the test.