At what temperature should blood cultures be sent in a hospital setting?

When to Send Blood Cultures in the Hospital Setting

Blood cultures should be sent when a patient has a temperature of >38.3°C (101°F) or when there are other signs of bloodstream infection, regardless of temperature. 1

Temperature Thresholds for Blood Culture Collection

The Infectious Diseases Society of America (IDSA) and the American Society for Microbiology (ASM) provide clear guidance on when blood cultures should be obtained:

• Primary temperature threshold: >38.3°C (101°F)
• Alternative criteria when temperature is not elevated:
  • Presence of chills
  • Hypotension (systolic blood pressure <90 mmHg)
  • Indwelling vascular catheter with suspected infection
  • Clinical suspicion of endocarditis
  • Neutrophil count >80% or WBC >18,000/mm³
  • Bands >5%
  • Platelets <150,000/mm³
  • Creatinine >2.0 mg/dL

Clinical Decision Algorithm

1. Major criteria (any one justifies blood cultures):

   • Temperature >39.5°C (103.0°F)
   • Indwelling vascular catheter
   • Clinical suspicion of endocarditis

2. Minor criteria (two or more justify blood cultures):

   • Temperature 38.3-39.4°C (101-102.9°F)
   • Age >65 years
   • Chills
   • Vomiting
   • Hypotension (systolic BP <90 mmHg)
   • Neutrophil percentage >80%
   • WBC count >18,000/mm³
   • Bands >5%
   • Platelets <150,000/mm³
   • Creatinine >2.0 mg/dL

This approach has been validated with a sensitivity of 97-98% for detecting true bacteremia 2.

Practical Considerations for Blood Culture Collection

• Volume: The most critical factor for detecting bacteremia

  • Adults: 20-30 mL per culture set (divided between bottles)
  • Children: Age and weight-appropriate volumes

• Timing: Collect before starting antibiotics whenever possible

  • For suspected endocarditis: 2-4 sets from different venipuncture sites
  • For suspected catheter-related infection: Paired cultures (one from catheter, one peripheral)

• Transport: Blood culture bottles should be transported to the laboratory as soon as possible

  • If immediate transport is not possible, bottles can be kept at room temperature for up to 12 hours without significant loss in yield 3
  • Avoid temperatures exceeding 25°C during transport or storage before incubation 3

Common Pitfalls to Avoid

1. Delaying blood culture collection until after antibiotics have been administered, which reduces sensitivity

2. Collecting inadequate blood volume, which is the most important variable affecting detection of bacteremia

3. Improper storage of blood culture bottles before incubation:

   • Temperatures exceeding 25°C can decrease pathogen recovery
   • Delays >12 hours before incubation may require special handling 3

4. Relying solely on fever for the decision to draw blood cultures:

   • Some patients with bacteremia may not present with fever
   • Consider the full clinical picture and other indicators of infection

5. Failing to collect the appropriate number of culture sets:

   • Single sets have lower sensitivity and make it difficult to interpret potential contaminants
   • For adults with suspected endocarditis or serious infection, 2-4 sets are recommended

By following these evidence-based guidelines, clinicians can optimize the diagnostic yield of blood cultures while avoiding unnecessary testing in patients at low risk for bacteremia.