What is the appropriate workup for a 9-month-old infant presenting with hematochezia (blood in stool)?

Workup for Blood in Stool in a 9-Month-Old Infant

In a 9-month-old infant with hematochezia, begin with a focused history and physical examination to assess hemodynamic stability, followed by stool testing for infectious pathogens and consideration of food protein-induced enterocolitis syndrome (FPIES), as most cases are benign and self-limiting. 1, 2

Initial Clinical Assessment

Immediate Stabilization

• Assess for hypovolemic shock immediately, as approximately 15% of acute presentations with bright red rectal bleeding can involve shock requiring aggressive fluid resuscitation. 1
• Check vital signs, blood pressure, heart rate, and signs of dehydration (skin turgor, mucous membranes, capillary refill) 3
• Obtain accurate body weight to assess fluid deficit 3

Critical History Elements

• Systematically assess for systemic symptoms including fever, abdominal pain, diarrhea, weight loss, or failure to thrive, as these suggest serious pathology requiring urgent gastroenterology referral. 1
• Document feeding history (breastfed vs. formula-fed), recent dietary changes, and timing of symptom onset 1, 4
• Ask about recent introduction of cow's milk or soy products, as FPIES is most commonly triggered by these allergens 1
• Inquire about personal or family history of easy bruising, excessive bleeding, or bleeding disorders 1
• Always consider child abuse when bleeding presents with other concerning features. 1

Physical Examination

• Perform a digital rectal examination when appropriate to assess for anal fissures, masses, or stool consistency. 1
• Examine for atopic eczema, as 38% of infants with rectal bleeding have concurrent eczema 4
• Look for signs of systemic illness, abdominal tenderness, or distension 1

Diagnostic Testing

Laboratory Workup

• Obtain stool testing for Shiga toxin-producing organisms (STEC), Salmonella, Shigella, Campylobacter, and Yersinia in infants with bloody diarrhea. 3
• STEC testing must use tests that detect Shiga toxin or genes encoding them, distinguishing O157:H7 from non-O157 strains 3
• Visual examination of stool to confirm blood presence 3
• Complete blood count with hemoglobin/hematocrit if significant bleeding is present 1, 5
• Basic metabolic panel if dehydration or significant bleeding is present 1

When to Avoid Imaging

• Imaging is NOT indicated for isolated microscopic hematochezia without proteinuria, dysmorphic red blood cells, or systemic symptoms. 6
• Most cases in this age group are benign and self-limiting, with bloody stools occurring irregularly for only a few days 4

When Colonoscopy is Indicated

• Reserve colonoscopy for patients with persistent bleeding, failure to thrive, severe systemic symptoms, or when diagnosis remains unclear after initial workup. 1, 2
• Colonoscopy in infants with rectal bleeding typically reveals focal mucosal erythema, aphthous ulcerations, and eosinophilic infiltration 4

Management Approach

Food Protein-Induced Enterocolitis Syndrome (FPIES)

• If FPIES is suspected (healthy-appearing infant with blood-streaked stools), initiate a cow's milk elimination diet as first-line treatment. 1, 7
• For breastfed infants, the mother should eliminate cow's milk and soy from her diet 7
• For formula-fed infants, switch to extensively hydrolyzed or amino acid-based formula 7
• Symptoms should resolve within 72-96 hours of starting the elimination diet. 7
• Diagnosis is confirmed by resolution with elimination and reappearance with reintroduction 7

Infectious Gastroenteritis Management

• Use oral rehydration solution (ORS) as primary treatment for most infants with gastroenteritis and dehydration. 3
• For severe dehydration (>5% dehydrated, lethargic, hypovolemic), initiate IV boluses of isotonic saline or Ringer's lactate 3
• NEVER give antibiotics if STEC is suspected or confirmed, as this increases risk of hemolytic uremic syndrome (HUS). 3
• Hold antibiotics until pathogen identification in most cases 3
• Do NOT use antidiarrheal agents (loperamide, kaolin-pectin, antimotility drugs) in infants with gastroenteritis. 3

Red Flags Requiring Urgent Intervention

• Hemodynamic instability despite fluid resuscitation 3
• Signs of sepsis or altered mental status 3
• Persistent or worsening bloody diarrhea 3
• Severe lethargy 3
• Monitor for hemolytic uremic syndrome development, especially if STEC is identified, as those producing Shiga toxin 2 carry higher HUS risk. 3

Common Pitfalls to Avoid

• Never assume hemorrhoids without proper evaluation, as symptoms attributed to hemorrhoids frequently represent other pathology. 1
• Do not rely on stool tests alone to diagnose FPIES, though they may show eosinophilic debris. 1
• It is essential to exclude upper GI source, as 10-15% of patients with severe hematochezia have an upper GI bleeding source. 1
• Do not continue cow's milk elimination diet indefinitely without proper challenge testing, as cow's milk allergy is less common than previously believed (only 18% in one study) 4

Prognosis

• Rectal bleeding in infants is generally benign and self-limiting, with most cases resolving within days to weeks. 2, 4
• Most children with FPIES can tolerate the trigger food within one year of life with excellent long-term prognosis 7
• Follow-up at 1 month and reassess for resolution of symptoms 4