The diagnosis of an IBD is primarily made with non-laboratory tests, in particular, a biopsy is considered the gold standard for diagnosis and for distinguishing between ulcerative colitis and Crohns disease. However, laboratory testing is an important tool for ruling out other causes of diarrhea, abdominal pain, and colitis. These causes can include viral or bacterial infections, parasites, medications, abdominal or pelvic radiation, colon cancer, and a variety of other chronic conditions, such as celiac disease and cystic fibrosis.
Tests that may be ordered to rule out other causes of diarrhea and gastrointestinal inflammation include:
- Stool culture to look for bacterial infection
- O&P (Ova and parasite) to detect parasites
- Clostridium difficile to detect toxin created by bacterial infection; may be seen following antibiotic therapy
- Fecal occult blood to look for blood in the stool due to causes such as infection, inflammation, and cancers
- Stool WBC to detect white blood cells in the stool, an indication of inflammation in the digestive tract
- Anti-tissue transglutaminase (anti-tTG) and other tests for celiac disease (see Celiac Disease Tests)
Tests that are not specific for IBD but may be done to detect and evaluate the inflammation and anemia associated with IBD include:
- ESR (erythrocyte sedimentation rate) to detect inflammation
- CRP (C-reactive protein) to look for inflammation
- CBC (complete blood count) to check for anemia
Tests that are not yet widely used but may be ordered fall into two groups: stool tests and antibody tests.
Two stool (fecal) tests are available that detect substances released by white blood cells. These test for:
These substances are associated with inflammation and with disease activity, severity, and relapse. They may be used to help distinguish between IBD and non-inflammatory disorders and also to monitor IBD. These tests are gaining attention as they may prove to be more sensitive than the current test for stool WBC.
Tests to detect antibodies that are frequently present in people who have IBD: one or more may sometimes be ordered to help distinguish between the two most common types of IBD, ulcerative colitis (UC) and Crohns disease (CD). They are not sensitive or specific enough to diagnose either condition, but they may give the doctor additional information. These biomarkers are not widely used clinically and their ultimate role has yet to be determined. They include:
- pANCA (Perinuclear anti-neutrophil cytoplasmic antibody). More common with UC, it is found in about 50% of those with UC but only about 5% to 20% of those with CD.
- ASCA (Saccharomyces cerevisiae antibodies), IgG and IgA. ASCA is more common with CD; it is found in about 40% to 50% of those with CD. ASCA IgG is found in about 20% of those with UC. ASCA IgA is found in less than 1% of those with UC.
- Anti-CBir1 (Clostridium species antibodies). Found to be associated with about 50% of Crohns disease cases.
- Anti-Omp C (Escherichia coli antibodies). Associated with rapidly progressing Crohns disease.
- Anti-I-2 (Pseudomonas fluorescens antibodies)
Several of these markers may be ordered together in a panel and overall findings evaluated. An example includes ordering ASCA, pANCA, and Anti-Omp C together to help differentiate CD from UC.
These tests are used to help diagnose and monitor UC and CD. They can be used to look for characteristic changes in the structure and tissues of the intestinal tract and to detect blockages. Care must be taken during an acute attack or flare-up of an IBD as there is a slight chance of perforating the bowel during testing.
- X-ray (abdominal). Barium contrast dye allows an evaluation of the intestines.
- Sigmoidoscopy. A slender tube is used to examine the last 2 feet of the colon.
- Colonoscopy. A slender tube is used to examine the entire colon; it includes a light and camera and can be used to take biopsies.
A biopsy may be performed during endoscopy or colonoscopy in which tissue samples are evaluated for inflammation and abnormal changes in cell structures. This test is considered the gold standard for diagnosis and for distinguishing CD from UC because of the characteristic changes that are seen.