What lab tests are recommended for a patient presenting with symptoms of a stuffy nose, diarrhea, fever, chills, and weakness?

Laboratory Testing for Patients with Stuffy Nose, Diarrhea, Fever, Chills, and Weakness

For a patient presenting with symptoms of stuffy nose, diarrhea, fever, chills, and weakness, a stool sample for culture-independent multiplex molecular diagnostics and blood tests including complete blood count, electrolytes, renal function, and C-reactive protein should be performed to identify the causative pathogen and assess disease severity.

Initial Assessment and Testing Strategy

Blood Tests

• Complete Blood Count (CBC) - Essential for all patients with fever and systemic symptoms 1

  • Helps assess for leukocytosis which may indicate bacterial infection
  • Lymphopenia may suggest viral infection (particularly noted in severe influenza cases)
  • Evaluates for anemia which may contribute to weakness

• Basic Metabolic Panel

  • Urea, creatinine and electrolytes - To assess for dehydration and renal impairment 1
  • Hypo/hypernatremia may be present due to diarrhea and dehydration

• Liver Function Tests - To evaluate for hepatic involvement 1

• C-reactive Protein (CRP) - Useful when bacterial superinfection is suspected 1

Stool Testing

• Diarrheal stool sample (preferred over rectal swab) for:

  • Culture-independent multiplex molecular diagnostics (gastrointestinal panel) 1, 2
  • This can detect multiple bacterial, viral, and parasitic pathogens simultaneously

• Specific testing based on clinical presentation:

  • If bloody diarrhea: Stool culture with specific testing for Shiga toxin-producing E. coli (STEC) 1, 2
  • If healthcare exposure or recent antibiotics: C. difficile testing 1, 2

Testing Selection Based on Symptom Pattern

The combination of respiratory symptoms (stuffy nose) with gastrointestinal symptoms (diarrhea) and systemic symptoms (fever, chills, weakness) suggests:

1. Viral gastroenteritis with concurrent upper respiratory infection

   • Norovirus often presents with vomiting, non-bloody diarrhea, and low-grade fever 1
   • Respiratory viruses can cause both respiratory and GI symptoms

2. Bacterial infection with systemic spread

   • Salmonella, Campylobacter, and Shigella can cause fever, chills, and diarrhea 1
   • These may require blood cultures if bacteremia is suspected 1

Special Considerations

• If fever is high or persistent: Blood cultures should be obtained to rule out bacteremia 1

• If symptoms have persisted >14 days: Consider parasitic infections and non-infectious causes such as inflammatory bowel disease 2

• For patients with severe illness (high fever, significant weakness, signs of dehydration):

  • More extensive testing including chest X-ray may be warranted to rule out pneumonia 1
  • Consider procalcitonin testing to help differentiate bacterial from viral infection

Common Pitfalls to Avoid

1. Relying solely on CBC for diagnosis - While leukocytosis may suggest bacterial infection, it has poor specificity for bacteremia in febrile patients 3

2. Collecting multiple stool specimens for C. difficile - A single diarrheal stool specimen is sufficient; multiple specimens do not increase yield 1

3. Starting empiric antibiotics before obtaining cultures - This may increase risk of complications in certain infections (e.g., HUS in STEC) and reduce diagnostic yield 2

4. Focusing only on infectious causes - Consider non-infectious etiologies if initial testing is negative or symptoms persist 2

By following this testing approach, clinicians can efficiently identify the causative pathogen and provide appropriate treatment while minimizing unnecessary testing and interventions.