What routine investigations should be performed in a patient presenting with fever?

Routine Investigations for Fever

For patients presenting with fever, obtain at least two sets of blood cultures (ideally 60 mL total) from different anatomical sites, perform a chest radiograph, and measure temperature using oral or rectal methods rather than less reliable techniques like axillary or tympanic measurements. 1

Core Laboratory Investigations

Blood Cultures - Essential First Step

• Collect at least two sets of blood cultures (ideally 60 mL total blood) sequentially from different anatomical sites without time intervals between them 1
• If central venous catheter is present: draw simultaneous cultures from both the catheter and peripheral sites to calculate differential time to positivity 1
• Sample at least two lumens if central line cultures are indicated 1
• Rapid molecular blood tests should only be used alongside traditional blood cultures, never as standalone tests 1

Imaging - Chest Radiograph is Standard

Perform a chest radiograph on all febrile patients as pneumonia is the most common infection causing fever in hospitalized patients 1. This is a best-practice statement with strong consensus despite the low positive predictive value of abnormal findings.

Procalcitonin - Risk-Stratified Approach

• Low to intermediate probability of bacterial infection: Measure procalcitonin in addition to clinical evaluation 1
• High probability of bacterial infection: Do NOT measure procalcitonin to rule out infection 1

This nuanced approach recognizes that procalcitonin has utility in uncertain cases but should not delay treatment when bacterial infection is clinically evident.

Context-Specific Investigations

Post-Surgical Patients

Perform CT imaging (coordinated with surgical team) if fever develops days after thoracic, abdominal, or pelvic surgery and initial workup fails to identify a source 1. This is particularly critical as surgical complications carry high morbidity.

Abdominal Evaluation - Selective Approach

• Do NOT routinely perform abdominal ultrasound in patients without abdominal symptoms, liver function abnormalities, or recent surgery 1
• DO perform formal abdominal ultrasound if any of the following are present:
  • Recent abdominal surgery
  • Abdominal symptoms or abnormal examination
  • Elevated transaminases, alkaline phosphatase, or bilirubin 1

Respiratory Symptoms Present

Test for viral pathogens using nucleic acid amplification panels if pneumonia is suspected or upper respiratory symptoms (cough) are present 1. Always test for SARS-CoV-2 based on community transmission levels 1.

Urinary Tract Evaluation

If pyuria is present and urinary tract infection suspected: replace the urinary catheter and obtain cultures from the newly placed catheter 1. This prevents contamination from colonized catheters.

Advanced Investigations for Unclear Etiology

When initial workup fails to identify a source:

• Consider 18F-FDG PET/CT if transport risk is acceptable (sensitivity 85-100%, though specificity varies 23-90%) 1
• Thoracic ultrasound may help identify pleural effusions or parenchymal pathology if chest radiograph is abnormal and expertise is available 1

Critical Pitfalls to Avoid

Temperature measurement matters: Oral or rectal temperatures are preferred over axillary, tympanic, or temporal artery methods which are unreliable 1. In critically ill patients with invasive devices, use central temperature monitoring (pulmonary artery catheter thermistors, bladder catheters, esophageal thermistors) 1.

Don't routinely use antipyretics for temperature reduction alone, as they don't improve mortality outcomes 1. Reserve them for patient comfort when specifically requested 1.

Avoid shotgun testing: The guidelines explicitly recommend AGAINST routine abdominal imaging without clinical indicators 1, recognizing that indiscriminate testing increases costs and false positives without improving outcomes.

Evidence Quality Note

These recommendations come from the 2023 Society of Critical Care Medicine and Infectious Diseases Society of America guidelines [1-1], representing the most current expert consensus. While most recommendations are based on low-quality evidence (reflecting the difficulty of conducting RCTs in febrile patients), the best-practice statements achieved 80% agreement from at least 75% of expert panelists, providing strong clinical consensus where randomized data is lacking.