What labs to order for a patient with recurring fever, nausea, vomiting, abdominal pain, and diarrhea?

Laboratory Evaluation for Recurrent Fever, Nausea, Vomiting, Abdominal Pain, and Diarrhea

For a patient with recurring fever, nausea, vomiting, abdominal pain, and diarrhea, a comprehensive stool analysis including culture-independent diagnostic testing and blood tests should be ordered based on the clinical presentation and risk factors. 1, 2

Initial Laboratory Evaluation

Stool Studies

• Multiplex PCR panel for enteric pathogens - provides rapid identification of multiple bacterial, viral, and parasitic pathogens 1, 2
• Stool culture - especially if the PCR panel is positive to isolate organisms for antimicrobial susceptibility testing 1
• Clostridioides difficile testing - particularly if patient has history of recent antibiotic use (within 8-12 weeks) 2
• Ova and parasite examination - especially for persistent symptoms or travel history 1, 2

Blood Tests

• Complete blood count (CBC) - to evaluate for leukocytosis, anemia, or thrombocytopenia 3
• Comprehensive metabolic panel - to assess liver function, electrolytes, and renal function 4
• Blood cultures - if fever is high or persistent, to rule out bacteremia 1
• C-reactive protein and/or erythrocyte sedimentation rate - to assess inflammatory response 5

Additional Tests Based on Clinical Presentation

If Severe Abdominal Pain is Present

• Amylase and lipase - to rule out pancreatitis 4
• Liver function tests - if right upper quadrant pain or hepatomegaly is present 1

If Persistent Fever is Present

• Blood cultures - to evaluate for enteric fever or bacteremia 1
• Thyroid function tests - especially with prolonged symptoms 4

For Specific Patient Populations

Immunocompromised Patients

• Extended parasite testing for:
  • Cryptosporidium
  • Cyclospora
  • Cystoisospora
  • Microsporidia
  • Mycobacterium avium complex
  • Cytomegalovirus 1, 2

Recent Travelers

• Specific parasite testing - especially for symptoms lasting >14 days 1, 2
• Malaria testing - if travel to endemic regions 1

If Part of an Outbreak

• Broader pathogen testing - coordinated with public health authorities 1

Interpretation of Results

• Interpret multiplex PCR results with caution as they detect DNA, not necessarily viable organisms 1, 2
• Culture confirmation is important for positive PCR results, especially for public health surveillance 1
• Consider clinical presentation when interpreting test results 2

Common Pitfalls to Avoid

1. Repeated C. difficile testing within 7 days during the same episode of diarrhea is not recommended 2

2. Failure to consider non-infectious causes such as inflammatory bowel disease, irritable bowel syndrome, or medication side effects 1, 4

3. Overlooking specific pathogens based on clinical presentation:

   • Bloody diarrhea: Consider STEC, Shigella, Salmonella, Campylobacter, E. histolytica 1
   • Persistent diarrhea: Consider parasitic infections like Cryptosporidium, Giardia, Cyclospora 1
   • Severe abdominal pain with minimal fever: Consider STEC, Salmonella, Campylobacter 1

4. Not collecting specimens properly - fresh diarrheal stool samples are optimal 2

5. Missing enteric fever - which may present with persistent fever but sometimes minimal diarrhea 1, 6

By following this structured approach to laboratory testing, clinicians can efficiently identify the cause of recurring fever, nausea, vomiting, abdominal pain, and diarrhea, leading to appropriate treatment and improved patient outcomes.