What should I request if I have a fever?

What to Request for Fever Evaluation

For any adult with fever, immediately obtain a chest radiograph and at least two sets of blood cultures from different anatomical sites before starting any antibiotics. 1, 2

Essential Initial Testing

Mandatory First-Line Tests

• Chest radiograph is recommended as a best-practice statement for all patients who develop fever 1, 2
• Blood cultures (minimum two sets from different anatomical sites, collected simultaneously without time interval between them) 1, 2, 3
• Complete blood count with differential to identify leukocytosis (>14,000 cells/mm³), left shift (band neutrophils ≥6% or >1,500/mm³), or elevated white blood cell count (≥15,000/mm³) as indicators of bacterial infection 1, 4

Additional Basic Laboratory Tests

• Urinalysis and urine culture if urinary symptoms are present or suspected 1, 2
  • For catheterized patients with pyuria: replace the catheter first, then obtain cultures from the newly placed catheter 2, 3
• Liver function tests (transaminases, alkaline phosphatase, bilirubin) 2
• Inflammatory markers: Consider procalcitonin (PCT) or C-reactive protein (CRP) only if bacterial infection probability is low-to-intermediate, not if probability is high 1, 2, 3

Risk Stratification Indicators

The following features predict higher likelihood of occult bacterial infection and should prompt more aggressive workup 4:

• Age ≥50 years
• Diabetes mellitus
• White blood cell count ≥15,000/mm³
• Band neutrophil count ≥1,500/mm³
• Erythrocyte sedimentation rate ≥30 mm/h

Patients with 2 or more of these features have 39-55% probability of occult bacterial infection, including bacteremia. 4

Imaging Based on Clinical Context

Recent Surgery Patients

• CT scan (thoracic, abdominal, or pelvic) in collaboration with surgical service if initial workup doesn't identify etiology 1, 2

Abdominal Symptoms or Abnormal Labs

• Formal diagnostic abdominal ultrasound if abdominal symptoms, abnormal physical exam, or elevated liver enzymes are present 1, 2
• Do NOT perform routine abdominal ultrasound in patients without abdominal signs, symptoms, or liver abnormalities 1, 2

Abnormal Chest Radiograph

• Thoracic bedside ultrasound to better identify pleural effusions and parenchymal pathology if expertise is available 1

Advanced Testing When Initial Workup Is Negative

If the etiology remains unclear after initial testing 1, 2:

• 18F-fluorodeoxyglucose PET/CT can be performed if transport risk is acceptable
• Consider additional serologic testing for region-specific infections (HIV, cytomegalovirus, Epstein-Barr virus, tuberculosis) 5

Critical Pitfall to Avoid

Never initiate empirical antibiotics before obtaining blood cultures. 3 Prior antibiotic use is a major cause of culture-negative infections and obscures diagnosis. Blood cultures must be drawn first from at least two different anatomical sites. 1, 2, 3

Temperature Measurement Method

For accurate fever documentation (≥38.3°C or ≥101°F) 1:

• Preferred: Central methods (pulmonary artery catheter thermistors, bladder catheters, esophageal balloon thermistors) when devices are already in place
• Acceptable: Oral or rectal temperatures
• Avoid: Axillary, tympanic, temporal artery, or chemical dot thermometers (less reliable) 1