What are the initial diagnostic tests for abdominal distention?

Initial Diagnostic Tests for Abdominal Distention

For patients presenting with abdominal distention, the initial diagnostic approach should include abdominal imaging and laboratory tests, with specific tests ordered based on the presence of alarm features, recent worsening symptoms, or abnormal physical examination findings. 1

Initial Evaluation

Laboratory Tests

• Complete blood count (CBC)
• Comprehensive metabolic panel (CMP)
• C-reactive protein
• Serum albumin
• Ferritin levels 2
• Stool Hemoccult test 1
• Consider stool testing for C. difficile and other pathogens when appropriate, especially in elderly patients with recent antibiotic use 2

Imaging Studies

• Abdominal X-ray: Initial imaging to assess for obstruction, volvulus, fecal loading, or increased intestinal gas 1, 2

  • Note: Plain abdominal radiography has limited diagnostic value for most abdominal pain but can be useful to identify severe constipation or obstruction 1

• Abdominal ultrasound: Particularly useful for detecting ascites and biliary pathology 2

  • Ultrasonography should be performed in questionable cases of ascites since physical examination and radiographic signs can be unreliable 3
  • Bedside ultrasound performed by clinicians has shown excellent diagnostic accuracy for small bowel obstruction with a positive likelihood ratio of 9.55 4

Further Testing Based on Clinical Presentation

For Suspected Functional Disorders

• Rome IV criteria should be used to diagnose primary abdominal bloating and distention 1
• Consider anorectal physiology testing if bloating and distention are thought to be related to constipation or difficult evacuation 1

For Suspected Malabsorption/Intolerance

• Carbohydrate enzyme deficiencies may be ruled out with dietary restriction and/or breath testing 1
• Serologic testing for celiac disease (tissue transglutaminase antibodies) 1
• Small bowel aspiration and glucose- or lactulose-based hydrogen breath testing for small intestinal bacterial overgrowth (SIBO) in at-risk patients 1

For Suspected Motility Disorders

• Gastric emptying studies if nausea and vomiting are present 1
• Whole gut motility studies only if treatment-refractory lower GI symptoms exist 1

Advanced Imaging When Indicated

• CT scan: Recommended when initial tests are inconclusive or when serious pathology is suspected 1, 2

  • CT is particularly useful for excluding a transition point in diffusely distended small bowel and may prevent unnecessary laparotomy 1

• MRI: Emerging technique for evaluation of abdominal distention that avoids ionizing radiation 1

Special Considerations

• In patients over 50 years, consider colonoscopy to rule out colorectal malignancy 2
• In women over 50 years with unexplained abdominal distention, consider ovarian cancer in the differential diagnosis 1
• In elderly patients, consider medication-induced causes (opioids, anticholinergics) 2

Common Pitfalls

• Relying solely on physical examination to diagnose ascites without confirmatory imaging 3
• Ordering gastric emptying studies routinely for bloating without accompanying nausea/vomiting 1
• Attributing distention to increased intestinal gas when studies show that visible abdominal distention is often due to abdominophrenic dyssynergia rather than actual gas accumulation 5
• Failing to consider serious underlying conditions like malignancy, especially in older adults 2

By following this diagnostic approach, clinicians can efficiently identify the cause of abdominal distention and develop appropriate management strategies to improve patient outcomes.