Acute-phase reactants, such as erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP), are sensitive markers of acute inflammation, but are nonspecific, and may also be less accurate in patients with chronic nutritional deficiencies, including hypoproteinemia.
Liver assessment is important but also nonspecific. It can uncover mild abnormalities in the transaminase levels in CD, or help identify the 10% to 15% of patient with UC who also have sclerosing cholangitis, an autoimmune disease of the biliary tract that may be even more devastating to the patient than UC itself.
A complete blood count and peripheral smear often uncover the microcytic anemia of iron deficiency, resulting from either chronic GI blood loss, poor intake of iron in the diet, or malabsorption of enteral iron. Macrocytic anemia can be seen in IBD patients with a history of terminal ileal resection or chronic disease, due to poor absorption of vitamin B12, or rarely in patients with proximal small bowel disease who malabsorb folic acid.
Lipase may be useful to check, because a small percentage of CD patients may manifest pancreatitis due to CD, or possibly due to medications commonly used for the treatment of IBD.
Stool samples looking for common bacterial pathogens in patients with a clinical history of potential exposure, and fecal leukocyte testing, are necessary to heighten the suspicion of IBD and to eliminate common acute causes of enterocolitis in previously healthy individuals. Ova and parasite testing is useful in this regard as well.
A spot test for fecal alpha-1-antitrypsin will uncover a protein-losing enteropathy, and in the differential diagnosis of these disorders, IBD is most common.
Serology: In the past several years, there has been a large body of work on specific antibodies commonly recovered from patients with IBD. Perinuclear anti-saccharomyces cervasiae antibody (pASCA) and perinuclear anti-neutrophil cytoplasmic antibody (pANCA) have been enthusiastically adopted as potential screening labs for suspected cases of IBD, as well as to help differentiate CD from UC when only colonic involvement is found, and when the histopathology is nonspecific. However, these antibodies have a low sensitivity (50%-65%) and do not replace clinical acumen when making the diagnosis of IBD.
Imaging studies can be useful, if often nonspecific in evaluation of IBD. Fluoroscopic evaluation with upper GI series and small bowel follow-through has been the gold standard for many years in the evaluation of suspected small bowel CD. Characteristic findings of separation of edematous bowel loops, coin-stacking appearance of prominent valvulae conniventes, and string-like narrowed areas of inflammation as well as fistula detection can be seen in these patients. Barium enema evaluation of the colon and terminal ileum may reveal absence of haustral markings, narrowed areas of luminal inflammation, or fistula formation connecting other abdominal or pelvic structures.
Computed tomography (CT) scanning is often performed in the acute care setting when a patient presents with acute or severe abdominal pain, and is most helpful when intraluminal contrast is ingested, so that luminal contents can be differentiated from extraluminal processes. CT scans are often read as showing mural thickening of an area of intestine, such as terminal ileum, colon, or even more proximal small intestine. Although a more chronic history coupled with isolated mural thickening of the ileum may raise suspicion of IBD, these radiographic findings are nonspecific, and can be seen in acute infectious illnesses as well as in IBD. Again, they need to be interpreted within the clinical context of the history and exam.
Endoscopy has been the gold standard method for diagnosis of IBD for more than 30 years in pediatrics. Esophagogastroduodenoscopy can examine the upper digestive tract lumen up to the ligament of Treitz, while colonoscopy can evaluate the entire colon and terminal ileum. Gross endoscopic findings of IBD include loss of vascular markings, friability, ulceration, edematous folds, luminal narrowing, pesudopolyp formation, and active bleeding. CD typically has a patchy distribution, manifesting skipped areas between actively inflamed areas, while UC is characteristically more contiguous, and limited to the colon. Occasionally, acute ileal findings can be seen with UC (“backwash ileitis”), but this is usually easily distinguishable from CD on histologic examination of ileal biopsies. UC often starts with proctitis only, or “left-sided” disease involving the rectum to the splenic flexure but sparing the rest of the more proximal colon. Pancolitis is also common in UC, but rectal sparing or exclusively right-sided inflammation is usually more prevalent in CD.
Histologic findings on biopsies obtained at endoscopy may overlap between CD and UC. The pathognomonic finding of noncaseating granulomas is seen in fewer than 30% of patients with CD, and transmural inflammation, typical of CD only, is found less often when endoscopic examination is undertaken earlier in the course of the disease. Crypt abscesses can be found in either CD or UC, and the population of white blood cells in the lamina propria may overlap in either disorder. More often than not, the diagnosis of CD versus UC is made based on the distribution of disease, as well as the clinical presentation, rather than the histologic findings alone