The principal question to be answered is whether the patients’ symptoms are related to inflammation from IBD, infections, strictures leading to bowel obstruction, irritable bowel syndrome or related to a condition of another abdominal organ. There is no single gold standard test that provides all the information that is needed for clinical decision making about a patient’s symptoms. Most of the time, a combination of tests is needed.

The options for testing include laboratory testing, radiographic imaging, and endoscopy.

A complete blood count (CBC) can be used to evaluate the patient’s overall health and detect a wide variety of disorders, including anemia, infection, and leukemia. On evaluation of the CBC, an acute or progressive decline in hemoglobin, even in the absence of overt bleeding, would suggest ongoing blood loss which would be concerning for inflammation. In addition, an elevated white blood cell (WBC) count, would be more concerning for active infection (possibly due to bowel inflammation or even an abscess) and prompt further evaluation. An elevated platelet count or thrombocytosis can suggest either infection or inflammation; however, it is not specific for these and can just be elevated in the presence of iron deficiency anemia. It is worth noting that the WBC can also be altered by treatments for IBD. For example, leukocytosis can occur with the use of steroids, and leukopenia can occur with immunosuppressants such as azathioprine and 6-mercaptopurine.

FCP has been extensively studied in the evaluation and monitoring of IBD. FCP levels are higher in patients with definite IBD compared to non-IBD controls, and in addition, elevated FCP is positively related to clinical disease activity and endoscopic grade of inflammation with high sensitivity and specificity [1–5]. FCP can also be used as a predictor of relapse [6] with a rise in FCP levels prior to the onset of symptoms. More severe disease phenotypes (those that have a worse future outcome) like stricturing disease were associated with even higher levels of FCP.

Many studies show that CRP is also associated with both clinical and endoscopic disease activity [6, 7]. However, CRP is not consistently elevated in all individuals with active IBD. Therefore, it is important to establish at the outset whether an individual is prone to demonstrating elevations in CRP in the setting of active disease; this will then determine it will be worthwhile to follow CRP as a measure of disease activity in a specific patient. Additionally, CRP is not specific for IBD and may be elevated in other inflammatory conditions.

Radiologic imaging remains an important tool in the monitoring of IBD. Cross-sectional imaging is a discipline of radiology that encompasses the use of a number of advanced imaging techniques that feature in common the ability to image the body in cross section. This discipline typically focuses on the diagnosis and characterization of abnormalities of the chest, abdomen, and pelvis. The scope of the discipline is broad and ranges from the assessment of emergency conditions and trauma to the detection and follow-up of malignancies. Primary imaging modalities include computed tomography (CT), magnetic resonance imaging (MRI), and ultrasound. The use of cross-sectional imaging, especially computed tomography (CT) studies such as CT of the abdomen and pelvis, has dramatically increased in general and specifically for IBD-related diagnoses [8].

The use of CT is widespread, and it has the advantage that CT studies can be obtained in a rapid fashion, allowing them to be used to quickly evaluate sick patients, especially in emergency departments. Reliable information can be obtained about abscesses, intestinal obstruction, intestinal perforation, and any other abdominal pathology that may explain patients’ symptoms. However, concerns have emerged about the long-term consequences of exposure to repeated amounts of ionizing radiation and possible contribution to a risk of malignancy [9, 10].

Magnetic resonance imaging (MRI) of the pelvis is key in the evaluation of patients with known or suspected fistulizing Crohn’s disease (CD), as well as abscesses in the pelvis and perineum as an adjunct to an examination under anesthesia (EUA). An EUA consists of visual inspection, palpation, and the passage of metal probes into fistula tracks under general anesthesia performed by an experienced surgeon. In addition, in patients with primary sclerosing cholangitis (PSC), magnetic resonance cholangiopancreatography (MRCP) helps evaluate and guide the management of biliary strictures.

Imaging with CT enterography or MR enterography is overall safe and useful. These cross-sectional imaging modalities complement laboratory testing and endoscopy in the initial evaluation, monitoring, and preoperative evaluation of patients with IBD [11]. Both tests allow easier determination of the extent of disease, especially small-bowel Crohn’s disease at the time of initial diagnosis, as well as determining the response to treatment with no significant differences in diagnostic accuracy between the two [12]. The advantage of MR enterography is that patients are not exposed to ionizing radiation; however, CT enterography is more commonly available.

Factors that may limit the use of CT in some patients include allergies to contrast reagents, concerns that preexisting chronic kidney disease may be worsened by intravenous contrast administration, and concerns about the cumulative dose of radiation received. Claustrophobia, prior metallic implants, and the increased risk of nephrogenic systemic fibrosis related to gadolinium administration in patients with chronic kidney disease may also limit the use of MRI.

In the era of CT and MR enterography, the use of small-bowel follow-through (SBFT) x-rays has declined, likely associated with a decline in the number of radiologists in community practice able to expertly perform and interpret SBFT. However, in geographical regions where expertise remains, SBFT remains an option in the mucosal evaluation of suspected or known small-bowel CD. It provides useful information about small-bowel luminal disease, strictures, and motility [13]. However, SBFT is limited in its ability to detect extramural complications, with the exception of intestinal fistulae.

The gold standard for the initial diagnosis of both ulcerative colitis (UC) and CD remains confirmation of the diagnosis with tissue pathology of tissues obtained in areas of the mucosa that are endoscopically abnormal. Once the diagnosis has been made, mucosal healing is increasingly accepted as an important endpoint for management of patients with IBD and is associated with sustained clinical remission [14, 15], prevention of complications, and reduced rates of surgery [16–18]. There are a number of scoring systems that integrate endoscopic findings into the assessment of patients including the Mayo score [19] and the Simple Endoscopic Score for Crohn’s Disease (SES-CD) [20]. These are mostly used in clinical trials and less often in routine clinical practice. However, these scoring systems reinforce the importance of endoscopy in evaluating symptoms, such as abdominal pain and diarrhea where the etiology is unclear, and determining the appropriate treatment response.