Priority Topic: Abdominal Pain

Key Feature 1c: Given a patient with abdominal pain, paying particular attention to its location and chronicity: Investigate in an appropriate and timely fashion. 
Skill: Clinical Reasoning, Selectivity
Phase: Investigation

In a couple of weeks I will be starting my rotation in the pediatric emergency department at the BC Children's Hospital and I am pretty well guaranteed to encounter a pediatric patient presenting with abdominal pain. A few months later, I'll be on my emergency medicine rotation at St Paul's Hospital and I am also certainly going to need to work up a patient presenting with abdominal pain there too. About a year after this, I will be an independent physician practicing in the community, and I will be fully responsible for knowing what to do if a patient walks into my office complaining of abdominal pain, be it acute or chronic, focal or generalised, in a pediatric or elderly patient, who is otherwise healthy or with multiple comorbidities. So no better time than now to have an approach to my workup of abdominal pain.

Per the differential diagnosis to acute, chronic, and pediatric abdominal pain (see previous blog post), here is my (UpToDate) approach to ordering investigations to working up the causes and consequences of abdominal pain. The UpToDate articles that have informed this approach are "Evaluation of the adult with abdominal pain in the emergency department," "Evaluation of the adult with abdominal pain," "Emergent evaluation of the child with acute abdominal pain," and "Chronic abdominal pain in children and adolescents: Approach to the evaluation."

Acute Abdominal Pain

• First-line labs to consider ordering:
  1. Beta-human chorionic gonadotropin (B-hCG)
  2. Capillary blood glucose (CBG) 
  3. Complete blood count, electrolytes, creatinine, urea, glucose +/- arterial blood gas (ABG)
  4. Lipase and liver function tests (ALT +/- AST, ALP +/- GGT, bilirubin)
  5. Urine dipstick

• First-line imaging to consider ordering: 
  1. Abdominal X-ray (AXR) (may be helpful to look for bowel obstruction, bowel perforation, or a radiopaque foreign body) 
  2. Ultrasound of the abdominal +/- pelvis (imaging of choice in pregnancy, or if AAA or gallbladder disease suspected, and can be useful for detecting free fluid/blood, hydronephrosis, pancreatitis, and venous thrombosis)
  3. CT (the study of choice in the evaluation of undifferentiated abdominal pain)

A note on investigations in general in the setting of acute abdominal pain: If a patient is otherwise healthy, investigations should only be ordered to confirm a clinically suspected diagnosis or to investigate for abdominal pain of unclear etiology. The threshold for ordering a broader range of tests should be lower for immunosuppressed patients and those with significant comorbidities (ex: diabetes, cancer, HIV, cirrhosis), as well as elderly patients who are unable to provide a comprehensive history (ex: if they are nonverbal or have an altered mental status).

Chronic Abdominal Pain
The natural history of chronic abdominal pain usually indicates there is less acutely worrisome pathology that in turn can be worked up in less of a shotgun approach

• ​​​Right upper quadrant pain
  1. First-line labs: CBC with differential (CBCd), electrolytes, Cr, urea, glucose, ALT +/- AST, ALP +/- GGT, bilirubin, lipase
  2. First-line imaging: Abdominal ultrasound
• Epigastric pain
  1. Same investigations as for right upper quadrant pain +/- abdominal ultrasound depending on your suspicion of hepatobiliary etiology
• Left upper quadrant pain
  1. Same investigations as for epigastric pain but also include an ultrasound or CT scan of the abdomen to assess for spleen pathology

A note on upper abdominal pain, no matter the region: Also consider the need to obtain an ECG and troponin level if the patient has cardiac risk factors or symptoms concerning for angina (ex: dyspnea, symptoms that occur with physical exertion), or a CXR or CT scan if there are symptoms (ex: dyspnea, cough) or signs on physical examination suggestive of pleural or pulmonary pathology.

• Lower abdominal pain
  1. First-line labs to consider ordering: 
     1. B-hCG
     2. CBCd
     3. Urine dipstick
  2. Imaging: Not necessarily indicated, but consider DDx
• Diffuse abdominal pain
  1. First-line labs: B-hCG (women of childbearing age), electrolytes (calculate anion gap), creatinine, urea, glucose, calcium, CBCd, lipase. Also check ALT, ALP, and bilirubin in older adult or immunosuppressed patients who may present atypically
  2. Imaging: Not necessarily indicated, but consider DDx
• For chronic abdominal pain in which preliminary workup has not yielded any useful findings, consider ordering the following labs: CBCd, electrolytes, Cr, urea, glucose, calcium, ALT, ALP, bilirubin, lipase, fecal calprotectin (sensitive for intestinal inflammation), anti-TTG + IgA

Pediatric Abdominal Pain
A repeated note on investigations in general in the setting of acute abdominal pain: If a patient is otherwise healthy, investigations should only be ordered to confirm a clinically suspected diagnosis or to investigate for abdominal pain of unclear etiology. The threshold for ordering a broader range of tests should be lower for immunosuppressed patients and those with significant comorbidities.

1. First-line labs to consider in acute abdominal pain: 
   1. Beta-human chorionic gonadotropin (B-hCG)
   2. Capillary blood glucose (CBG) 
   3. Complete blood count, electrolytes, creatinine, urea, glucose +/- ABG
   4. Lipase and liver function tests (ALT, ALP, bilirubin)
   5. Urine dipstick
   6. Rapid strep antigen testing or bacterial throat culture for GAS (if assoc pharyngeal findings)
2. First-line imaging to consider in acute abdominal pain include: AXR, US, and CT abdomen (Imaging is indicated if clinical picture suspicious for trauma, peritonitis, obstruction, mass, distention, or focal tenderness/pain. If clinical picture highly suspicious for acute appendicitis, consult surgeon first.)
3. For chronic abdominal pain consider the following investigations: CBCd, electrolytes, glucose, creatinine, ALT, ALP, bilirubin, lipase, calcium, albumin, total protein, anti-TTG + IgA, fecal calprotectin, c-reactive protein (CRP), stool for culture + sensitivity, clostridium difficile antigen, ova + parasites (x 3), H pylori stool or breath test

There is so much to know about when and when not to order specific tests, far more than I've included here, and this doesn't even include how to interpret them! But this is a place to start, to capture the most worrisome and most common causes of abdominal pain.