The following is an overview of the tests that help diagnose and monitor IBD. It also attempts to answer the practical questions that you may have before you undergo testing
There are two major types of laboratory tests, which can be broken down into routine tests and antibody tests.
Your doctor may request certain routine blood tests, such as a CBC (complete blood count), which helps detect inflammation and anemia, as well as monitor for side effects of certain medications you may take. Blood electrolyte testing measures sodium, potassium and other minerals that can be depleted in IBD-associated diarrhea. A low iron or vitamin B12 level can lead to anemia and may indicate decreased absorption from Crohn’s disease that affects the small intestine. Liver function tests help screen for liver and bile duct abnormalities seen in some patients with IBD. Finally, stool studies are done to determine whether patients have treatable bacterial infections that can trigger a flare-up of IBD or mimic IBD. It is important for your doctor to have all of this information before recommending other tests or changing your treatment.
Sometimes a definitive diagnosis between ulcerative colitis or Crohn’s disease involving the colon alone (Crohn’s colitis) cannot be made. This occurs in approximately 10-15% of patients. These unclear cases are called “indeterminate colitis” or IBD of undetermined type (IBD-U). For these patients, there are new blood tests that may help. These serological tests detect antibodies that may form in the blood. The standard IBD antibodies are named “perinuclear anti-neutrophil antibody” (pANCA) and “anti-Saccharomyces cervisiae antibody” (ASCA). Many patients with ulcerative colitis have the pANCA antibody in their blood, but not the ASCA antibody. For many Crohn’s patients, the opposite is true: the ASCA antibody is present, while the pANCA is not (Image). Unfortunately, some patients have neither antibody in their blood, and some Crohn’s patients may have only the “ulcerative colitis” pANCA antibody in their blood! In such cases, the search for newer antibody markers such as the anti-flagellin “CBir1” test can be helpful. These blood tests can help your doctor determine which condition is more likely, which may help in making decisions regarding medications or surgery. The McGill IBD research group is actively involved in research for better serological tests.