Blood Culture Indications

Author: Michelle Lin, MD
Updated: 8/17/2012

Blood cultures indications: Does this adult patient with suspected bacteremia require blood cultures?

Bacteremia = true-positive bacterial presence in bloodstream

  • Approximately 50% (+) blood cultures are false (+) from contaminants
  • Overall 4.1-7.3% incidence of true (+) blood cultures
Condition Pretest probability of bacteremia
Cellulitis 2%
Ambulatory outpatient 2%
Community acquired pneumonia 7%
Community-onset fever requiring hospitalization 13%
Pyelonephritis 19-25%
Severe sepsis 38%
Acute bacterial meningitis 53%
Septic shock 69%

Risk stratifying for bacteremia (excludes immunocompromised/endocarditis)

Finding Positive LR Negative LR
Chills 1.6 (1.3-1.8) 0.84 (0.77-0.90)
Chills + febrile patient 2.2 (1.4-3.3) 0.56 (0.41-0.76)
Severity of chills
  • Shaking
  • Moderate
  • Mild
  • None

  • 4.7 (3.0-7.2)
  • 1.7 (1.0-2.8)
  • 0.61 (0.26-1.4)
  • 0.24 (0.11-0.55)
  • Temperature
  • ≥ 40.0 C
  • ≥ 39.0 C
  • ≥ 38.5 C
  • ≥ 38.0 C

  • 0.3 (0.13-1.0)
  • 1.1 (0.79-1.6)
  • 1.4 (1.1-2.0)
  • 1.9 (1.4-2.4)

    • 1.1 (1.0-1.2)
    • 0.95 (0.83-1.1)
    • 0.50 (0.3-0.82)
    • 0.54 (0.38-0.78)
    Elevated WBC (cutoffs at 10K-15K) ≥ 1.7 ≥ 0.60
    Platelet count < 150,000 2.0-2.1 0.68-0.91
    Presence of SIRS (inpatient study) 1.8 (1.6-2.0) 0.09 (0.03-0.26)
    Shapiro prediction rule (ED study) 1.3 (1.2-1.4) 0.08 (0.04-0.17)

    Systemic inflammatory response syndrome (SIRS)

    At least 2 of following:

    • Temperature <36°C or >38°C
    • Heart rate >90 bpm
    • Respiratory rate > 22 / min, or pCO2 <32 mmHg on ABG
    • WBC <4K or >12K, or >10% bands

    Shapiro clinical prediction rule for bacteremia

    If suspect infection, blood cultures indicated if 1 major OR 2 minor criteria:

    Major

    • Endocarditis suspicion
    • Temperature >39.4°C
    • Indwelling vascular catheter

    Minor

    • Temperature 38.3°C - 39.3°C
    • Age > 65 years
    • Chills
    • Vomiting
    • SBP <90 mmHg
    • WBC >18K
    • Creatinine >2 mg/dL

    References

    • Coburn B, Morris AM, Tomlinson G, Detsky AS. Does this adult patient with suspected bacteremia require blood cultures? JAMA. 2012 Aug 1;308(5):502-11. doi: 10.1001/jama.2012.8262. [PubMed]