What is the appropriate evaluation and management for a 34‑year‑old presenting with acute abdominal pain and diarrhea?

Evaluation and Management of a 34-Year-Old with Abdominal Pain and Diarrhea

Immediate Assessment and Risk Stratification

Begin by rapidly assessing vital signs for fever, tachycardia, tachypnea, hypotension, or altered mental status to identify potential organ failure requiring immediate resuscitation. 1

• Establish intravenous access and initiate fluid resuscitation if signs of sepsis or shock are present 1
• Check for hypotension with hypoperfusion indicators (elevated lactate, oliguria, altered consciousness) which signal septic physiology 1
• Assess hydration status, as dehydration increases risk of life-threatening illness, especially in acute diarrhea 2

Focused History—Key Discriminating Features

Obtain a detailed clinical and exposure history focusing on symptom onset, stool characteristics, and epidemiologic exposures. 2

Timing and Character

• Acute onset (hours to days) raises concern for infectious gastroenteritis, inflammatory bowel disease, or bowel obstruction 1
• Pain that improves or worsens with defecation and is linked to altered stool patterns suggests irritable bowel syndrome 1
• Recent gastrointestinal infection or antibiotic exposure can precipitate post-infectious IBS in approximately 10% of patients 1

Red-Flag Features to Exclude

• Fever with bloody diarrhea suggests invasive bacterial infection (Salmonella, Shigella, Campylobacter, STEC) or inflammatory bowel disease 2
• Severe abdominal cramping or tenderness with bloody stools warrants stool testing for bacterial pathogens and Shiga toxin 2
• Recent antibiotic exposure raises concern for Clostridioides difficile infection 2
• Nocturnal diarrhea, unexplained weight loss, or blood in stools suggest organic disease rather than functional disorders 2

Epidemiologic Clues

• Attendance or work in child care centers, long-term care facilities, or food service requires outbreak reporting per jurisdictional guidelines 2
• Recent travel or contact with travelers from enteric fever-endemic areas with febrile illness warrants blood cultures 2

Physical Examination

Perform abdominal examination specifically assessing for peritoneal signs and dehydration severity. 1

• Abdominal rigidity (guarding) indicates peritonitis and mandates immediate surgical consultation 1
• Pain disproportionate to physical findings should raise suspicion for mesenteric ischemia 1
• Assess for clinical dehydration (dry mucous membranes, decreased skin turgor, tachycardia) to guide rehydration strategy 2

Laboratory Evaluation

Order baseline complete blood count, C-reactive protein, and stool studies based on clinical presentation. 1

Essential Initial Tests

• Complete blood count to assess for leukocytosis or anemia 1
• C-reactive protein or ESR for inflammatory markers 1
• Serum electrolytes, creatinine, and glucose to assess metabolic derangements 2

Stool Testing Indications

Obtain stool cultures for Salmonella, Shigella, Campylobacter, and STEC testing in patients with fever, bloody stools, severe abdominal cramping, or signs of sepsis. 2

• Test for C. difficile toxin PCR if recent antibiotic exposure or healthcare-associated diarrhea 2, 3
• Fecal calprotectin is indicated in patients younger than 45 years with diarrhea; values ≥250 µg/g strongly suggest inflammatory bowel disease and should trigger colonoscopy 1, 3
• Consider ova and parasites testing based on travel history or persistent symptoms 3

When Shiga Toxin-Producing Organisms Are Suspected

• Use diagnostic approaches that detect Shiga toxin (or genes encoding them) and distinguish E. coli O157:H7 from other STEC 2
• Sorbitol-MacConkey agar or chromogenic agar is recommended to screen for O157:H7 STEC 2

Imaging Strategy

Contrast-enhanced CT of the abdomen and pelvis is the gold-standard imaging for non-localized abdominal pain when organic pathology is suspected. 1

When to Image

• Severe or persistent pain despite initial management 1
• Signs of peritonitis, obstruction, or perforation 1
• Concern for inflammatory bowel disease complications (abscess, stricture) 3

Alternative Imaging

• Point-of-care ultrasound is appropriate when CT is unavailable or in resource-limited settings 1
• Plain abdominal radiographs have limited utility and should be reserved for suspected bowel obstruction 1

Rehydration and Supportive Care

Oral rehydration solution (ORS) is first-line therapy for mild to moderate dehydration in adults with acute diarrhea. 2

Rehydration Protocol

• ORS should be administered until clinical dehydration is corrected 2
• Isotonic intravenous fluids (lactated Ringer's or normal saline) are indicated for severe dehydration, shock, altered mental status, or ORS failure 2
• Once rehydrated, replace ongoing stool losses with ORS until diarrhea resolves 2

Nutrition

• Resume age-appropriate usual diet immediately after rehydration is completed 2

Pharmacologic Management

Antimotility Agents

Loperamide may be given to immunocompetent adults with acute watery diarrhea, but should be avoided in suspected inflammatory diarrhea or diarrhea with fever. 2

• Do not give antimotility drugs to patients with bloody stools, fever, or suspected toxic megacolon 2
• Theoretical risks exist that high-dose loperamide may predispose to toxic dilatation, especially in C. difficile infection 2

Antiemetics

• Ondansetron may facilitate tolerance of oral rehydration in patients with significant vomiting 2

Probiotics

• Probiotic preparations may be offered to reduce symptom severity and duration in immunocompetent adults with infectious or antimicrobial-associated diarrhea 2

Antispasmodics for Functional Symptoms

• If IBS is suspected after excluding red flags, antispasmodic (anticholinergic) agents are recommended for pain that worsens after meals 1
• Tricyclic antidepressants may be considered for frequent pain in IBS patients 1

Antibiotic Therapy

Do not routinely administer antibiotics for undifferentiated abdominal pain and diarrhea. 1

When Antibiotics Are Indicated

• Confirmed intra-abdominal abscess 1
• Overt sepsis or signs of systemic infection 1
• Specific identified bacterial pathogen requiring treatment per local guidelines 2
• C. difficile infection confirmed by toxin PCR (vancomycin or fidaxomicin) 2, 3

Coverage Considerations

• If empiric antibiotics are needed for suspected intra-abdominal infection, cover gram-negative bacteria and anaerobes 1

Differential Diagnosis Framework

Most Likely Diagnoses in This Age Group

1. Infectious gastroenteritis (viral, bacterial, or parasitic) 2, 4
2. Irritable bowel syndrome (post-infectious or functional) 2, 1
3. Inflammatory bowel disease (Crohn's disease or ulcerative colitis) 3
4. Celiac disease (if chronic symptoms) 2, 1

Less Common but Serious Considerations

• Mesenteric ischemia (though less likely at age 34 without risk factors) 1
• Small bowel obstruction (if history of prior abdominal surgery) 2, 1
• Appendicitis (if pain localizes to right lower quadrant) 1

When to Refer or Escalate Care

Immediate surgical consultation is indicated for signs of peritonitis (rigidity, rebound tenderness), hemodynamic instability, or suspected bowel obstruction. 1

• Gastroenterology referral if inflammatory bowel disease is suspected based on elevated fecal calprotectin or persistent symptoms 3
• Consider colonoscopy if fecal calprotectin ≥250 µg/g or alarm features are present 1, 3

Common Pitfalls to Avoid

• Do not delay stool testing in patients with fever or bloody diarrhea, as early pathogen identification guides appropriate therapy 2
• Avoid opioids for chronic or functional abdominal pain, as they cause narcotic bowel syndrome, dependence, and increased mortality 1
• Do not dismiss subtle peritoneal signs, as they often precede intestinal infarction 1
• Loperamide should not be given before excluding infection in patients with fever, bloody stools, or severe systemic symptoms 2

Follow-Up and Reassessment

• Reassess in 3–5 days for clinical improvement 3
• Repeat imaging if symptoms worsen or fail to improve 3
• If functional disorder (IBS) is diagnosed after excluding organic disease, avoid repetitive testing as it reinforces illness behavior 5