What labs should be ordered for a 3-year-old with 2 weeks of diarrhea and intermittent fever?

Laboratory Testing for a 3-Year-Old with 2 Weeks of Diarrhea and Intermittent Fever

For a 3-year-old with 2 weeks of diarrhea and intermittent fever, stool testing should be performed for bacterial pathogens including Salmonella, Shigella, Campylobacter, Yersinia, C. difficile, and STEC, along with evaluation for parasitic causes since symptoms have persisted beyond 14 days.

Initial Assessment and Specimen Collection

• Optimal specimen: Fresh diarrheal stool sample (takes shape of container) is strongly preferred over rectal swabs 1
• Timing: Collect specimen as soon as possible during a diarrheal episode
• Quantity: Single specimen is generally sufficient, though multiple specimens may increase yield for some pathogens 2

Recommended Laboratory Tests

First-line Tests (Essential):

1. Bacterial stool culture for:

   • Salmonella
   • Shigella
   • Campylobacter
   • Yersinia (especially important with persistent abdominal pain)
   • STEC (Shiga toxin-producing E. coli) 2

2. Stool examination for parasites:

   • Microscopy for ova and parasites
   • Specific testing for Giardia lamblia, Cryptosporidium, and Cyclospora 2
   • Particularly important since symptoms have persisted >14 days 2

3. C. difficile testing:

   • Consider if child has had recent antibiotic exposure
   • Use toxin detection or nucleic acid amplification test (NAAT) 2
   • Note: C. difficile testing is appropriate in children ≥2 years with prolonged diarrhea 2

Second-line Tests (Based on Clinical Features):

1. Blood tests:

   • Complete blood count (CBC) with differential
   • Basic metabolic panel to assess electrolyte abnormalities and renal function
   • C-reactive protein (CRP) or ESR to assess inflammation

2. Viral studies:

   • Consider testing for rotavirus and enteric adenovirus, especially if symptoms are consistent with viral gastroenteritis 3

Special Considerations

• Persistent symptoms (>14 days) suggest possible parasitic infection, inflammatory bowel disease, or other non-infectious causes 2
• Molecular diagnostic panels (multiplex PCR) may be considered for more rapid and comprehensive detection of multiple pathogens simultaneously 2
• Blood cultures are not routinely indicated unless there are signs of sepsis or systemic infection 2

Interpretation and Follow-up

• If all initial tests are negative, consider:
  • Non-infectious causes such as inflammatory bowel disease (IBD) or irritable bowel syndrome (IBS) 2
  • Lactose intolerance (especially after an infectious episode)
  • Celiac disease
  • Rare congenital diarrheal disorders if symptoms persist 4

Important Caveats

• Do not repeat C. difficile testing within 7 days during the same diarrheal episode 2
• Do not test asymptomatic patients for C. difficile 2
• Do not routinely perform antimicrobial susceptibility testing unless treatment is indicated based on severity or specific pathogen identification
• Avoid empiric antimicrobial therapy for uncomplicated diarrhea while awaiting test results, as this may worsen certain infections (e.g., STEC) 2

By following this systematic approach to laboratory testing, you can efficiently identify the cause of prolonged diarrhea and fever in this 3-year-old child and guide appropriate management to improve outcomes.