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 of IBD
- Monitor IBD disease activity and therapeutic response
Most laboratory tests used for IBD diagnosis are nonspecific; however, these tests can aid in identifying inflammation associated with IBD. Definitive diagnosis of IBD typically involves imaging and endoscopic evaluation.
Complete Blood Count
The American College of Gastroenterology (ACG), European Society for Pediatric Gastroenterology, Hepatology, and Nutrition (ESPGHAN), and 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.
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 will be elevated 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 albumin, transaminases (aspartate or alanine aminotransferase), and gamma-glutamyl transferase (yGT). Albumin may be decreased in patients with IBD. Transaminases and yGT may be increased and are recommended to evaluate patients for extraintestinal disease, but 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, 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; it has been found to correlate well with the level of mucosal inflammation, and can also be used as a screening test to help distinguish between IBD and irritable bowel syndrome (IBS). 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 caveat is that fecal biomarkers may have high variability between different sample collections from a single patient.
A negative fecal calprotectin result and a low pretest probability of disease may be sufficient to rule out a diagnosis of IBD.
The ACG and ESPGHAN/NASPGHAN 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 (see Thiopurine Therapy-Related Testing below).
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, immunization status, and vitamin D tests. See Monitoring section below 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 accumulation of active thiopurines. Phenotype testing should not be performed in patients already receiving treatment with thiopurines because results will be falsely low. In addition, the current TPMT phenotype may not reflect the future phenotype, particularly in patients who received blood transfusions within 30-60 days of testing.
Guidelines for thiopurine dosing are published 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. See Monitoring 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 the activity of disease 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 (primary response failure) or who stop responding to treatment (secondary response failure) should be evaluated using therapeutic drug monitoring to determine the cause of response failure and to guide clinical decisions. Some patients develop neutralizing antidrug antibodies (ADAs) that affect response to treatment, whereas others will manifest immunogenicity to TNF antagonist drugs (eg, adalimumab, infliximab). See the table below for clinical interpretation of tests used to monitor treatment with adalimumab and infliximab.
Therapeutic drug monitoring is not indicated for patients who are receiving maintenance regimens but are in remission.
Clinical Interpretation of Adalimumab/Infliximab and Antibody Testing Results
||Neutralizing Antibody Titer
||Subtherapeutic dose (nonimmune-mediated failure)
Consider higher dosage of adalimumab or shortening the dosing interval
||Neutralizing antibodies may be responsible for failure (immune-mediated failure)
Consider alternate anti-TNF-α drug
||Adalimumab/infliximab activity detected and no neutralizing antibodies present – likely a mechanistic failure
Consider alternate therapy (non-anti-TNF-α drug)
||Subtherapeutic dose (nonimmune-mediated failure)
Consider intensification of therapy
||Future retesting suggested to rule out decreasing activity and/or increasing neutralizing antibodies
NOTE: Suggested target trough concentrations for reactive monitoring of patients with active IBD on maintenance therapy is ≥5 µg/mL for infliximab and ≥7.5 µg/mL for adalimumab. The AGA makes no recommendation regarding the use of routine, proactive therapeutic drug monitoring in adults with quiescent IBD treated with anti-TNF-α agents. In the presence of sufficient trough concentrations, results of antibody testing should not guide treatment decisions.