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)
Shaking Chills	4.7 (3.0-7.2)
Moderate Chills	1.7 (1.0-2.8)
Mild Chills	0.61 (0.26-1.4)
No Chills	0.24 (0.11-0.55)
≥ 40.0 C	0.3 (0.13-1.0)	1.1 (1.0-1.2)
≥ 39.0 C	1.1 (0.79-1.6)	0.95 (0.83-1.1)
≥ 38.5 C	1.4 (1.1-2.0)	0.50 (0.3-0.82)
≥ 38.0 C	1.9 (1.4-2.4)	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]