What lab tests should be done for a patient presenting with fever after traveling to Indonesia?

Essential Laboratory Tests for Fever in Travelers Returning from Indonesia

For patients with fever after traveling to Indonesia, the most critical laboratory tests are three malaria blood films (thick and thin) taken 12-24 hours apart, complete blood count, dengue testing (PCR or serology), and blood cultures. 1

Initial Laboratory Workup

Immediate Testing (First 24 Hours)

• Malaria blood films (thick and thin smears) - first of three specimens 1, 2

  • Must be repeated at 12-24 hour intervals for a total of three specimens
  • Negative predictive value: platelet count >190 x 10^9/L has 97% negative predictive value for malaria 3

• Complete blood count (CBC) with differential 1

  • Look for thrombocytopenia (<150,000/μL) - highly suggestive of malaria or dengue
  • Leukopenia may suggest viral infection like dengue
  • Eosinophilia may indicate helminth infection or Katayama syndrome

• Blood cultures (before antibiotics) - essential for diagnosing enteric fever 1

  • Positive in approximately 5% of febrile returning travelers 4

• Dengue testing 1, 2

  • PCR if within 1-8 days of symptom onset
  • IgM serology if >5 days since symptom onset

• Basic metabolic panel and liver function tests

  • Look for hyperbilirubinemia (5-7 times more likely in malaria) 2

Additional First-Line Testing

• Chest X-ray if respiratory symptoms are present 1
• Urinalysis and urine culture to rule out urinary tract infection
• Stool culture - positive in 17% of febrile returning travelers 3
• HIV testing - recommended based on 3% positivity rate in febrile travelers 4

Second-Line Testing (Based on Clinical Presentation)

For Persistent Fever

• Follow-up malaria films (days 2-3) - even if initial tests are negative 1, 5
• Serological testing for:
  • Chikungunya (PCR early on, or IgM/IgG from 5-7 days) 2
  • Typhoid/paratyphoid fever
  • Rickettsial diseases

For Specific Symptoms

• For eosinophilia: Investigate for schistosomiasis, strongyloidiasis, filariasis 2
• For respiratory symptoms: Sputum culture, respiratory viral panel
• For neurological symptoms: Lumbar puncture, brain imaging, Japanese encephalitis serology

Interpretation Considerations

• Thrombocytopenia and hyperbilirubinemia have high positive likelihood ratios for malaria (3-11 and 5-7 respectively) 2
• Cross-reactions between flavivirus antibodies (dengue, Japanese encephalitis) can occur - vaccination history is important for interpretation 2
• Rapid diagnostic tests (RDTs) for malaria can be valuable adjuncts but should not replace microscopy 6
• Consider that 10% of returning travelers with fever have more than one diagnosis 4

Common Pitfalls to Avoid

1. Failing to obtain adequate malaria blood films - three negative films 12-24 hours apart are needed to rule out malaria 1
2. Relying solely on rapid diagnostic tests - RDTs have limitations including false negatives with low parasite density 6
3. Overlooking non-malarial causes - diarrheal illness is actually more common than malaria in returning travelers 2, 3
4. Delaying empiric treatment in severely ill patients while awaiting test results 1
5. Not considering multiple diagnoses - 10% of febrile returning travelers have more than one diagnosis 4

Remember that approximately 26% of returning travelers with fever have potentially life-threatening illnesses, with the strongest risk factors being CRP ≥100 and platelet count ≤140 4. This underscores the importance of comprehensive and timely laboratory evaluation.