What X-ray should be ordered for a constipated patient, especially with a history of abdominal surgery, inflammatory bowel disease, or on medications like opioids or anticholinergics?

Plain Abdominal X-ray for Constipation

Order a plain abdominal radiograph (KUB) only when you need to exclude bowel obstruction, perforation, or toxic megacolon in severely symptomatic patients—not for routine constipation diagnosis or management. 1

When to Order an Abdominal X-ray

High-Risk Patients Requiring Imaging

Plain abdominal radiography is indicated when:

• Severe symptoms suggest complications like bowel obstruction, perforation, or toxic colon distension 1
• Pain-predominant symptoms during an acute episode to exclude bowel obstruction and other abdominal pathology 1
• Acutely ill patients with suspected ileus or mechanical obstruction 1
• Red flag features including old age, complex surgical history, prior small bowel obstruction, abdominal malignancy, vomiting, or inability to pass flatus 2

Specific Clinical Contexts

• Cancer patients: Plain abdominal X-ray may be useful to image the extent of fecal loading and exclude bowel obstruction, though it is limited as a standalone tool 1
• Inflammatory bowel disease (Crohn's disease): Plain radiograph is useful in patients with severe symptoms for detection of bowel obstruction, perforation, or toxic colon distension 1
• Suspected fecal impaction: X-ray can show the extent of fecal loading, particularly when digital rectal examination suggests impaction 1, 3

When NOT to Order an Abdominal X-ray

Avoid routine abdominal radiography for:

• Simple constipation diagnosis: Constipation is a clinical diagnosis that does not require imaging confirmation 2, 4
• Treatment planning in uncomplicated cases: Plain films do not significantly affect ED management, and treatment often contradicts radiographic findings 2
• Routine assessment: History and digital rectal examination provide sufficient information to begin treatment in most cases 3

Key Evidence Against Routine Use

• In a study of 1,142 ED patients with constipation, abdominal radiography did not significantly affect management—55% of patients with no/mild stool burden were still diagnosed with constipation and treated, while 42% with moderate/large stool burden received no treatment 2
• Fecal loading on radiography does not exclude more serious diagnoses 2
• Radiologists and clinicians agree that constipation is a clinical diagnosis, with radiologists finding X-rays inaccurate at quantifying stool burden 4

Alternative Diagnostic Approach

Initial Assessment Without Imaging

For most constipated patients, begin with:

• Clinical evaluation: Assess defecation frequency, stool consistency (Bristol Stool Scale), and associated symptoms 5
• Digital rectal examination: Identify rectal impaction, which may require suppositories, enemas, or manual disimpaction 1
• Medication review: Discontinue constipating medications (opioids, anticholinergics, antidepressants) when possible 1
• Laboratory tests: Rule out metabolic causes (hypercalcemia, hypokalemia, hypothyroidism, diabetes mellitus) 1

Advanced Imaging When Needed

If symptoms persist or complications are suspected:

• CT abdomen/pelvis: Preferred for acutely ill patients to rule out intra-abdominal complications like abscess or to distinguish mechanical obstruction from ileus (>90% sensitivity and specificity) 1, 6
• MR enterography: Preferred for inflammatory bowel disease assessment, particularly small bowel disease 1
• Colonic transit studies: For chronic constipation with persistent symptoms despite treatment, use radiopaque marker studies rather than plain films 1, 3

Common Pitfalls to Avoid

• Do not delay surgical consultation while waiting for imaging if peritoneal signs, hemodynamic instability, or clinical deterioration are present 6
• Do not assume normal X-ray excludes serious pathology: History and physical examination should exclude simple constipation before attributing symptoms to benign causes 2
• Do not use X-ray findings alone to guide treatment: Clinical assessment should drive management decisions, not radiographic stool burden 2, 4
• Recognize that elderly or immunocompromised patients may not show typical inflammatory responses even with serious complications 6