Ulcerative colitis is an inflammatory bowel disease (IBD). Unlike Crohn's disease (another IBD), ulcerative colitis (UC) occurs only in the colon and affects only the superficial, mucosal lining. Symptoms of UC usually present first in the rectum and can make their way up through the entire colon (pancolitis). A distinguishing feature of UC is an uninterrupted swath of inflamed, ulcerated intestine.
Differentiating between UC and Crohn's disease is an important factor in treating the diseases. Because they share many symptoms, differentiation can be difficult and invasive. There is no definitive blood test for UC.
Complete Blood Count (CBC)
A complete blood count (CBC) is often performed when diagnosing IBD. This test measures the amount and maturity of a variety of components in the blood, including red blood cells (RBCs), white blood cells (WBCs) and platelets. This test can also detect infection and anemia.
Results of high WBCs in the blood indicate inflammation somewhere in the body. A positive result for anemia may be the result of excessive bleeding in the colon, which is a symptom of UC.
Antibody Tests
Antibodies are immunoglobulin proteins that play an important role in the body's immune system response to antigens (such as a viruses, toxins or bacterium). When the body detects a foreign substance, it creates antigen-specific antibodies to attach to that substance. These antibody-antigen complexes serve as markers that the immune system can follow to find and destroy the invader.
Antibody tests detect the presence (or absence) of certain antibodies in the blood, as well as the level of antibodies present.
pANCA
Until recently, there were no antibody tests for ulcerative colitis. A new test--the perinuclear anti-neutrophilic cytoplasmic antibody (pANCA)--is not 100 percent conclusive for UC (some Crohn's disease patients show positive results as well), but a high ratio of UC patients test positive for the protein.
Cigna, in its medical care coverage policy, says pANCA has been found to be present in up to 70 percent of UC patients, while its presence is found in only 10 percent to 40 percent of patients with Crohn's disease.
ASCA
According to the updated Ulcerative Colitis Practice Guidelines for Adults published in 2004 in the American Journal of Gastroenterology, a second antibody test--the anti-Saccharomyces cervisiae antibody (ASCA)--can aid in differentiating between UC and Crohn's disease. Patients who tested positive for pANCA and negative for ASCA had a "positive predictive vale of 75% for UC." Those patients who tested negative for pANCA and positive for ASCA "had a positive predictive value of 86% for the diagnosis of Crohn's disease."
Blood Tests for Ulcerative Colitis
Cigna and the American College of Gastroenterology recognize that the antibody tests can be helpful in differentiating between the two diseases. They also agree that there are more definitive testing methods and that blood tests, if given, should not be the only factor considered for diagnosis.
