The clinician must initially adopt a broad differential diagnosis that becomes more focused as the investigation progresses. The history should inquire about the characteristics of abdominal pain including the onset, duration, location, nature, radiation, associated features, and relieving and aggravating factors. Establishing the duration of pain is very useful in narrowing the differential diagnosis. Chronic abdominal pain is defined as constant or intermittent pain occurring for greater than 6 months. Acute abdominal pain is when pain has been occurring for up to several days, and sub-acute abdominal pain is from several days to 6 months. After establishing chronicity, the location, nature, and radiation of pain should be determined to help focus attention to certain pathologies. Upper abdominal pain can arise from biliary, pancreatic, gastric, and duodenal pathology. Mid-abdominal pain likely originates from the small bowel (e.g., Crohn’s disease, celiac disease, bacterial overgrowth, partial small bowel obstruction, chronic mesenteric ischemia). Lower abdominal pain arises from the colon (e.g., irritable bowel syndrome, colitis), bladder, or reproductive organs. It is important to differentiate between constant and intermittent chronic abdominal pain. While intermittent pain can have many causes, constant abdominal pain results from only a few gastrointestinal etiologies (Table 3.2). The presence of aggravating and relieving factors can be quite informative. Pain that is positional in nature is likely to be of musculoskeletal origin. Worsening of pain with eating is typical in peptic ulcer disease, chronic mesenteric ischemia, and in the presence of biliary and pancreatic pathologies. Relief with bowel movements is expected with constipation and irritable bowel syndrome (IBS). Pain related to menstruation may signify a gynecological cause. The clinician should probe for coexisting symptoms such as nausea, vomiting, diarrhea, blood in stools, and systemic symptoms like fever or rash. The presence of diarrhea suggests IBS, chronic pancreatitis, inflammatory bowel disease, celiac disease, and bacterial overgrowth. “Alarm” symptoms of fever, weight loss, night sweats, appetite, or nocturnal awakening often indicate organic pathology.

Rare medical causes of abdominal pain should be considered when structural etiologies are ruled out. Recurrent attacks of fever, joint pain, and abdominal pain suggest familial Mediterranean fever [2]. Recurrent attacks of abdominal pain, tachycardia, constipation, and dark urine suggest acute intermittent porphyria. The presence of hyponatremia, hyperkalemia, and hyperpigmentation should raise suspicion for adrenal insufficiency. Hereditary angioedema should be considered in patients with intermittent abdominal pain who have a history of recurrent angioedema without urticaria. History of exposure, metallic taste in mouth, and cognitive impairment should direct attention to heavy metal poisoning. The presence of coexisting medical illnesses may also suggest a cause of abdominal pain. A history of vasculopathy raises suspicion of chronic mesenteric ischemia. A history of physical or sexual abuse is common in patients with functional gastrointestinal disorders [3]. A family history of gastrointestinal malignancy, pancreatic disorders, or inflammatory bowel disease should be elicited.

A complete abdominal examination includes inspection, auscultation, percussion, and palpation. Surgical scars on inspection should be noted. Identification of a bruit on auscultation may indicate chronic mesenteric ischemia. Light and deep palpation should be performed to check for masses, ascites, hernias, and organomegaly. Observing the patient’s response to palpation can be helpful in differentiating functional from organic disease. A closed eye sign and stethoscope sign are seen more in functional gastrointestinal disorders. A closed eye sign is when patients close their eyes during examination [4], in contrast to patients with acute abdominal pain whose eyes open in fearful anticipation. The stethoscope sign is the detection of less tenderness during pressure with a stethoscope than with palpation [5]. Hover sign and Carnett’s sign are seen in abdominal wall pain. Hover sign is when lightly touching the area of pain and patient guards the area with his hand or grabs the examining hand [6]. Carnett’s sign is increased abdominal tenderness when the patient tenses their abdominal muscles [7]. Patients with chronic abdominal pain may still present with an acute abdomen and care should be taken to look for peritoneal signs of rebounding and guarding.

It is important to also perform a complete physical examination looking for systemic disease. Signs of malnutrition, vitamin deficiency, and skin changes can signify organic illness. Skin rashes can be helpful in narrowing the diagnosis. Dermatitis herpetiformis is associated with celiac disease (Fig. 3.1). Erythema nodosum, pyoderma gangernosum, and sweets syndrome may be seen in inflammatory bowel disease (Fig. 3.2). Acanthosis nigricans, Leser–Trélat sign, hypertrichosis lanuginosa, Tylosis, and Tripe palm can signify underlying malignancy.

Laboratory test abnormalities are common in patients with organic pathology, while normal lab tests are expected in patients with functional bowel disorders. Routine laboratory evaluation includes complete blood cell count (CBC). Anemia can raise suspicion of IBD, celiac disease, or gastrointestinal malignancies. Elevated platelet counts and white blood cell count can be seen in inflammatory diseases. Additional laboratory testing should be based on history and physical examination. Testing for Helicobacter pylori antibody should be considered in patients with upper abdominal pain. Celiac serology testing should be considered in those with suspicion of celiac disease. Liver function tests should be checked in those with suspicion of biliary pathology. If recurrent pancreatitis is considered, amylase and lipase should be checked.