What investigations should be done for a patient presenting with fever for 2 days?

Investigations for Fever of 2 Days Duration

For a patient presenting with fever for 2 days, a focused diagnostic approach should include blood cultures, complete blood count, basic metabolic panel, and chest radiography as the initial investigations.

Initial Laboratory Investigations

Essential First-Line Tests

• Blood cultures: At least two sets (ideally 60 mL of blood total) should be collected from different anatomical sites without time interval between them 1
• Complete blood count with differential: To assess for leukocytosis, lymphopenia, thrombocytopenia, or eosinophilia which may indicate specific infectious processes 1, 2
• C-reactive protein (CRP) and/or erythrocyte sedimentation rate (ESR): Particularly useful if bacterial infection probability is low to intermediate 1
• Basic metabolic panel: To evaluate renal function and electrolyte abnormalities
• Liver function tests: To assess for hepatic involvement which may indicate specific infections 1

Additional Laboratory Tests Based on Clinical Presentation

• Procalcitonin (PCT): Consider if bacterial infection probability is low to intermediate and no clear focus of infection is identified 1
• Urinalysis and urine culture: Especially important if urinary symptoms are present or in patients with pyuria 2
• Serum sample for serology: Store for potential later testing based on clinical evolution 1

Imaging Studies

• Chest radiograph: Recommended as a standard investigation for all patients with fever 1
• Consider additional imaging based on symptoms:
  • Abdominal ultrasound: If abdominal symptoms or abnormal liver function tests are present 1
  • CT scan: For patients who have recently undergone thoracic, abdominal, or pelvic surgery and no etiology is readily identified 1

Special Considerations

Travel History

• For patients with recent travel to tropical regions:
  • Malaria testing: Thick and thin blood films plus rapid diagnostic test (RDT) for any patient who has visited a tropical country within the past year 1
  • Testing for viral pathogens: Consider viral nucleic acid amplification tests if respiratory symptoms are present 1
  • SARS-CoV-2 PCR: Based on community transmission levels 1

Tick Exposure

• If tick exposure is suspected:
  • PCR for tickborne illnesses: Consider early testing for RMSF, Ehrlichia, or Anaplasma 2
  • Consider empiric doxycycline while awaiting test results if clinical suspicion is high 2

Diagnostic Algorithm

1. Assess vital signs and perform targeted physical examination

   • Focus on skin (rashes), neck stiffness, lymphadenopathy, abdominal examination
   • Look for localizing signs of infection

2. Order initial laboratory tests

   • Blood cultures (two sets)
   • CBC with differential
   • CRP/ESR
   • Basic metabolic panel
   • Liver function tests
   • Urinalysis

3. Order chest radiograph

4. Additional testing based on clinical findings

   • Respiratory symptoms → viral testing panels
   • Abdominal symptoms → abdominal ultrasound
   • Travel history → malaria testing, specific serology
   • Tick exposure → tickborne illness testing

Common Pitfalls to Avoid

• Failing to obtain adequate blood cultures before starting antibiotics
• Overlooking travel history which may significantly alter the differential diagnosis
• Relying on presence of rash to diagnose or exclude certain infections
• Delaying transfer to emergency department when concerning features (altered mental status, hypotension) are present
• Not repeating physical examinations as new findings may emerge over time

Red Flags Requiring Urgent Attention

• Neck stiffness with fever (possible meningitis)
• Altered mental status
• Hypotension or signs of shock
• Respiratory distress
• Petechial or purpuric rash

By following this systematic approach to investigating fever of short duration, clinicians can efficiently identify the cause and initiate appropriate management to improve patient outcomes.