What are the necessary laboratory and radiologic studies, contraindications, assessment, and treatment approaches for a patient presenting with constipation?

Constipation: Laboratory and Radiologic Studies, Contraindications, Assessment, and Treatment

Laboratory Studies Required

In the absence of alarm symptoms, only a complete blood count is necessary—metabolic panels including glucose, calcium, and thyroid-stimulating hormone should not be routinely ordered unless specific clinical features warrant them. 1, 2

• CBC is the single mandatory test for all patients with constipation to detect anemia 1, 2
• Corrected calcium levels and thyroid function tests should only be checked if clinically suspected based on other symptoms (e.g., hypercalcemia symptoms, thyroid dysfunction signs) 3, 1
• Avoid routine metabolic testing without clinical indication, as it increases costs without proven benefit 1

Radiologic Studies: When to Order and When to Avoid

Plain Abdominal X-ray

• Limited utility as a standalone tool, but may be useful to image the extent of fecal loading and exclude bowel obstruction 3
• Should generally be avoided due to poor diagnostic value 1

Colonoscopy Indications

Colonoscopy should only be performed if alarm features are present or age-appropriate colorectal cancer screening has not been completed. 1, 2

Alarm features requiring colonoscopy include: 1, 2, 4

• Blood in stool or rectal bleeding
• Anemia detected on CBC
• Unintentional weight loss
• Abrupt/sudden onset of constipation
• Age >50 years without previous colorectal cancer screening
• Palpable abdominal or rectal mass

Specialized Functional Testing

Order colonic transit studies and anorectal function tests only after a 1-2 week trial of fiber supplementation and over-the-counter laxatives has failed. 1, 5

• Anorectal manometry and balloon expulsion test should be performed first when digital rectal examination suggests pelvic floor dysfunction or when patients report prolonged straining, need for perineal/vaginal pressure to evacuate, or digital evacuation of stool 1, 2
• Colonic transit studies (six marker study) are indicated only if anorectal tests are normal and symptoms persist despite treatment 1, 5

Contraindicated Studies and Procedures

Enemas and Suppositories: Absolute Contraindications

Enemas are contraindicated in the following clinical scenarios: 3

• Neutropenia or thrombocytopenia
• Paralytic ileus or intestinal obstruction
• Recent colorectal or gynecological surgery
• Recent anal or rectal trauma
• Severe colitis, inflammation, or infection of the abdomen
• Toxic megacolon
• Undiagnosed abdominal pain
• Recent radiotherapy to the pelvic area

Medication Contraindications

• Linaclotide is contraindicated in patients <2 years of age and those with known or suspected mechanical gastrointestinal obstruction 6
• Lubiprostone is contraindicated in patients with known or suspected mechanical gastrointestinal obstruction 7
• Bulk laxatives (psyllium) are not recommended for opioid-induced constipation 3
• Magnesium and sulfate salts should be used cautiously in renal impairment due to risk of hypermagnesemia 3

Assessment Approach

History Taking

A thorough medical history must elicit specific bowel pattern details: 3, 1

• Date of last defecation, frequency, and stool consistency
• Presence or absence of urge to defecate
• Sensation of complete versus incomplete evacuation
• Blood or mucus on defecation
• Need for digital manipulation to assist evacuation
• Fecal incontinence or rectal leakage

Assess for contributing factors: 3, 1

• Medication review: opiates, anticholinergics, calcium channel blockers
• Eating and drinking habits
• Physical activity level relative to illness stage
• Privacy and comfort for defecation
• Comorbidities: heart failure, chronic pulmonary disease, irritable bowel syndrome, diverticular disease

Physical Examination

Digital rectal examination is mandatory and must assess: 3, 1, 2

• Resting sphincter tone and squeeze augmentation
• Puborectalis muscle contraction during squeeze
• Perineal descent during simulated evacuation
• Patient's ability to "expel my finger" during simulated defecation
• Presence of impacted feces, hemorrhoids, masses, or stenosis
• Tenderness or obstruction

Abdominal examination should evaluate: 3, 1

• Distension, masses, liver enlargement
• Tenderness and bowel sounds (increased or decreased)

Perineal inspection should check for: 3, 1

• Skin tags, fissures, prolapse
• Anal warts, perianal ulceration

Patient-Reported Outcome Measures

• Use the Bowel Function Index (BFI) as a validated tool for assessing constipation severity, particularly for opioid-induced constipation 3, 1
• Consider medication for BFI score ≥30 points with no response to initial laxatives 3, 1

Treatment Algorithm

First-Line: Prevention and Self-Care

Best practice balances prevention strategies with prescribed laxative therapy: 3

• Ensure privacy and comfort for defecation
• Positioning: use small footstool to assist gravity and exertion
• Increase fluid intake
• Increase activity and mobility within patient limits (even bed to chair)
• Anticipatory management when opioids are prescribed

Second-Line: Pharmacologic Therapy

When laxatives are needed, preferred first-line options include: 3

• Osmotic laxatives: PEG (17g/day preferred), lactulose, or magnesium/sulfate salts
• Stimulant laxatives: senna, cascara, bisacodyl, sodium picosulfate

For elderly patients, PEG (17g/day) offers efficacy with good safety profile 3

Fecal Impaction Management

When digital rectal examination identifies a full rectum or fecal impaction: 3

• Suppositories and enemas are preferred first-line therapy (if not contraindicated)
• In absence of suspected perforation or bleed, perform disimpaction through digital fragmentation and extraction
• Follow with maintenance bowel regimen to prevent recurrence

Opioid-Induced Constipation

Unless contraindicated by pre-existing diarrhea, all patients receiving opioid analgesics should be prescribed a concomitant laxative prophylactically. 3

• First-line: osmotic or stimulant laxatives
• Avoid bulk laxatives (psyllium)
• Combined opiate/naloxone medications reduce OIC risk 3
• For unresolved OIC, peripherally acting μ-opioid receptor antagonists (PAMORAs) may be valuable 3

Refractory Constipation

For patients failing over-the-counter laxatives after 1-2 weeks: 1, 5

• Proceed to anorectal testing if defecatory disorder suspected
• Biofeedback therapy is first-line definitive treatment for confirmed defecatory disorders, with success rates exceeding 70% 2
• Consider intestinal secretagogues (lubiprostone, linaclotide) or prokinetic agents for slow-transit constipation 5
• Colectomy may be considered for refractory slow-transit constipation in specific patients 5

Critical Pitfalls to Avoid

• Do not rely solely on digital rectal examination to exclude defecatory disorders—a normal exam does not rule them out 1
• Do not skip structural evaluation in high-risk patients with alarm symptoms, age >50 without screening, or abrupt onset 1
• Do not proceed to specialized testing before attempting empiric fiber/laxative trial for 1-2 weeks 1, 5
• Avoid liquid paraffin for bed-bound patients and those with swallowing disorders 3