Inflammatory bowel disease (IBD) includes a spectrum of chronic disorders that affect the gastrointestinal (GI) tract and is believed to develop as a result of immunologic, environmental, and genetic influences. , Crohn disease (CD) and ulcerative colitis (UC) are the primary subtypes of IBD; a third subtype that cannot be categorized as either CD or UC based on features at diagnosis is referred to as IBD, unclassified (IBD-U) (sometimes referred to as “indeterminate colitis”). , IBD can vary in severity; a higher inflammatory burden and greater anatomic extent of disease characterize more severe IBD. Early diagnosis is important for disease management, but distinguishing between the IBD subtypes can present a diagnostic challenge, particularly because CD and UC can manifest as atypical phenotypes. A combination of clinical tools—including laboratory tests, clinical examination and patient history, and endoscopic and radiologic findings—is used to establish diagnosis and to determine the extent and severity of disease. Laboratory testing is also used for disease management and for therapeutic drug monitoring, which is particularly important in IBD to optimize clinical outcomes. Laboratory tests for IBD include serum and fecal inflammatory markers and stool culture tests to rule out enteric infections. , Due to their limited sensitivities, serologic tests play an adjunct role in IBD diagnosis and/or risk stratification.
Quick Answers for Clinicians
Differentiating between Crohn disease (CD) and ulcerative colitis (UC) can be challenging, but features such as rectal bleeding and anemia are more common in UC than CD, whereas perianal involvement, stenosis, abscesses, and fistulas are more common in CD than UC. Distinguishing the two diseases generally requires endoscopic evaluation and/or imaging. Serologic testing may help to differentiate between inflammatory bowel disease (IBD) subtypes (eg, antiglycan antibodies are more frequently seen in CD than in UC), but this testing is not highly sensitive, which limits its usefulness. Serologic antibody testing is not currently recommended by the American College of Gastroenterology (ACG) for IBD diagnosis. , The ACG also discourages the use of serologic testing to predict disease course or severity in patients with UC. However, serologic response to certain microbial antigens is a recognized risk factor for progression in CD; therefore, serologic testing may aid in the risk stratification of patients with CD. Refer to the Serologic Markers section for additional testing information.
Although some genetic variants are associated with specific inflammatory bowel disease (IBD) phenotypes, genetic testing has not been found to provide significant benefits in IBD diagnosis or prognosis. , Genetic testing is primarily used for therapeutic decision-making in IBD because variants in TPMT and NUDT15 genes can affect how patients metabolize thiopurine drugs used for IBD treatment. Refer to the Thiopurine Therapy-Related Testing section for additional information.
Diagnosis of inflammatory bowel disease (IBD) in pediatric patients is complicated by the fact that studies in recent years have reported atypical phenotypes of all three subtypes of IBD in children and adolescents, which points to a need to more accurately define the subtypes. A new subtype of ulcerative colitis (UC) in pediatric patients is referred to as atypical UC. Diagnosis is more challenging when disease onset occurs in infancy and when the disease primarily affects only the colon; it is more difficult to distinguish between Crohn disease (CD), UC, and IBD, unclassified (IBD-U) in these cases. A greater percentage of IBD cases (up to 33%) are diagnosed as IBD-U in patients younger than 2 years. As these patients become older, a more definitive diagnosis of CD or UC is often made.
Indications for Testing
Laboratory testing for IBD is appropriate to:
- Diagnose individuals who present with abdominal pain, diarrhea or bloody stool, frequent/urgent bowel movements, tenesmus, fatigue, weight loss, anemia, fever, fistulas, and/or growth failure (in children)
- Guide treatment decisions in patients with an established diagnosis
- Monitor disease activity and therapeutic response
Most laboratory tests used for IBD diagnosis are nonspecific; however, the following tests can help to identify inflammation associated with IBD. Definitive diagnosis of IBD typically involves imaging and endoscopic evaluation.
The American College of Gastroenterology (ACG), the European Society for Pediatric Gastroenterology, Hepatology, and Nutrition (ESPGHAN), and the North American Society for Pediatric Gastroenterology, Hepatology, and Nutrition (NASPGHAN) recommend that initial laboratory testing for IBD include a CBC. CBC results may reveal anemia and increased platelet counts in patients with IBD.
ESPGHAN also recommends measuring albumin, transaminases (aspartate or alanine aminotransferase), and gamma-glutamyl transferase (GGT) concentrations in the evaluation of suspected IBD in pediatric patients. Albumin concentrations may be decreased in patients with IBD. Transaminases and GGT concentrations may be increased, and the measurement of these markers is recommended to evaluate patients for extraintestinal disease. However, increased levels may be associated with causes other than extraintestinal illness.
Measurement of fecal calprotectin, a calcium-binding protein, is useful to screen for intestinal inflammation associated with disease activity (eg, at initial presentation or relapse). , , Fecal calprotectin testing is a noninvasive substitute for endoscopy if the procedure is unavailable or unfeasible. Fecal calprotectin is considered among the most useful of the inflammatory markers for IBD. Concentrations of fecal calprotectin have been found to correlate well with the level of mucosal inflammation, and a normal fecal calprotectin result has a high negative predictive value for IBD. Fecal calprotectin measurement can also be used as a screening test to help distinguish between IBD and irritable bowel syndrome (IBS). A negative fecal calprotectin result and a low pretest probability of disease may be sufficient to rule out a diagnosis of IBD.
Fecal lactoferrin, an iron-binding protein, is another useful marker of intestinal inflammation in IBD ; however, more evidence is available for fecal calprotectin. One potential limitation of fecal biomarkers is that different samples collected at different times from a single patient may vary highly in terms of fecal marker concentrations.
The ACG recommends tests for inflammatory markers, such as C-reactive protein (CRP) or erythrocyte sedimentation rate (ESR), in the initial workup for IBD. Serum CRP and ESR concentrations will be increased in some patients with IBD , ; however, both CRP and ESR are nonspecific markers of inflammation. CRP is the more sensitive and specific marker for detecting acute phase inflammation. ESPGHAN and NASPGHAN recommend that initial testing for IBD in pediatric patients include at least two tests for inflammatory markers, such as CRP and ESR.
The ACG, ESPGHAN, NASPGHAN, and the British Society of Gastroenterology (BSG) recommend testing to identify fecal pathogens and Clostridium difficile in cases of clinical suspicion for IBD. , , , However, an enteric infection may not rule out a diagnosis of IBD because such an infection may initiate IBD. The ACG recommends stool culture testing for Salmonella, Shigella, Yersinia, Campylobacter, and C. difficile, as well as testing for Giardia lamblia if exposure is suspected.
Serologic marker testing is not currently recommended by the ACG for IBD diagnosis or prognosis due to its limited sensitivity and usefulness in differentiating between IBD subtypes. , Some specific markers, such as anti-Saccharomyces cerevisiae antibodies (ASCAs) and perinuclear antineutrophil cytoplasmic antibodies (pANCAs), have been associated with IBD. ASCAs are more common in CD and less common in UC, whereas pANCAs are more common in UC cases and less common in CD. Patients with IBD-U are often negative for both antibody types. Other serologic markers associated with IBD include laminaribioside carbohydrate (immunoglobulin G [IgG]), mannobioside carbohydrate (IgG), and chitobioside carbohydrate (IgA) antibodies.
Although serologic marker testing is not considered useful to predict disease course or severity in UC, serologic response to certain antigens is a recognized risk factor for progression in CD. , Therefore, serologic testing may aid in risk stratification of patients with CD.
Although some genetic variants are associated with specific IBD phenotypes, genetic testing is not currently recommended for IBD diagnosis. , No one genetic variant has a high enough frequency in CD to be considered helpful for diagnosis. Genetic markers in UC have been only modestly helpful in determining the course or severity of disease. , However, genetic testing has a role in guiding IBD treatment (refer to the Thiopurine Therapy-Related Testing section).
A workup for IBD relies on a variety of diagnostic tools, such as endoscopic, radiographic, pathologic, and histologic findings, in addition to laboratory tests. Endoscopic examination, in conjunction with histologic confirmation, helps determine the extent of disease and provides baseline data for later assessment of therapeutic response.
Tests Before Treatment Initiation
In addition to the tests used for diagnosis, some specific tests are recommended before treatment initiation. The European Crohn’s and Colitis Organisation (ECCO) recommends that pretreatment laboratory testing include electrolyte, renal function, iron level, and vitamin D tests. Refer to the Monitoring section for tests used to monitor treatment.
Anti-JC Virus Antibodies
Testing for antibodies to JC virus is recommended in patients with CD; natalizumab should be used for CD treatment only in patients negative for anti-JC virus antibodies.
Thiopurine Therapy-Related Testing
Pharmacogenetic testing before treatment initiation may be helpful to guide therapeutic decisions, particularly because treatment failure due to individual differences in medication response is not uncommon in IBD. Thiopurine drugs are commonly used in treating IBD.
The American Gastroenterological Association (AGA) recommends either phenotype or genotype testing in adults beginning thiopurine therapy. TPMT and NUDT15 gene variants (detected by genotype testing), as well as reduced TPMT enzyme activity (determined by phenotype testing), are associated with a greater risk of myelosuppression in response to treatment with thiopurines due to the accumulation of active thiopurines. Phenotype testing should not be performed in patients already receiving treatment with thiopurines because results will be falsely low.
Guidelines for thiopurine dosing are published by the Clinical Pharmacogenetics Implementation Consortium and can help avert myelosuppression. In patients with TPMT and/or NUDT15 variants or patients with demonstrated TPMT enzyme activity deficiency, a significant reduction in dose may be needed. Pharmacogenetic testing does not replace the need for clinical monitoring of patients treated with thiopurine drugs.
Monoclonal Antibody Therapy-Related Testing
Before treatment with monoclonal antibodies such as antitumor necrosis factor (anti-TNF) agents, the ACG recommends testing for inactive opportunistic infections such as tuberculosis (TB). Evaluation for viral hepatitis is also recommended before anti-TNF treatment is introduced. Refer to the Monitoring section for information about testing during treatment with monoclonal antibodies.
Tests to Monitor Disease
Patients with IBD should be monitored for complications, relapse, and anxiety and depressive disorders associated with IBD. Long-term IBD is associated with an increased risk of colorectal cancer and dysplasia, most likely due to long-term inflammation, and patients must be monitored for the development of these conditions as well.
Laboratory tests for monitoring in IBD include fecal and serum marker testing (in conjunction with imaging and endoscopic evaluation) to evaluate inflammatory responses. Quantitative fecal calprotectin and fecal lactoferrin tests are sensitive markers that can be used to gauge IBD activity, recurrence, and relapse, although they may be more useful tools in UC than in CD. Serum CRP is not specific for inflammation in IBD but may aid in monitoring disease activity and therapeutic response.
Tests to Monitor Treatment
CBCs should be monitored during treatment. Additional tests may be indicated for specific types of treatment. For example, repeat testing for anti-JC virus antibodies is recommended at least every 6 months in patients receiving natalizumab for CD because of the risk of progressive multifocal leukoencephalopathy caused by the JC virus. Liver and renal function monitoring are recommended during treatment with drugs such as sulfasalazine or mesalamine for UC. Testing for cytomegalovirus colitis using sigmoidoscopy is recommended by the International Consortium for Health Outcomes Measurement (ICHOM) in adult patients with colitis that is unresponsive to treatment with corticosteroids; however, this testing is not recommended in children.
Patients who do not respond initially or who stop responding to treatment with monoclonal antibody therapeutics (eg, adalimumab, infliximab) should be evaluated using therapeutic drug monitoring. Refer to the Laboratory Testing for Monoclonal Antibody Therapeutics topic for more information about monitoring strategies for monoclonal antibody drugs.
ARUP Laboratory Tests
Semi-Quantitative Indirect Fluorescent Antibody (IFA)/Semi-Quantitative Enzyme Immunoassay (EIA)
Components: ASCA, IgG; ASCA, IgA; antineutrophil cytoplasmic antibody (ANCA), IgG
Semi-Quantitative Enzyme-Linked Immunosorbent Assay
Semi-Quantitative Indirect Fluorescent Antibody (IFA)
Quantitative Electrochemiluminescence Immunoassay (ECLIA) with Acid Dissociation
Quantitative Electrochemiluminescent Immunoassay (ECLIA) with Acid Dissociation
Enzyme-Linked Immunosorbent Assay
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