Blood Culture 

Updated: Aug 01, 2014
  • Author: Christopher P Kellner, MD; Chief Editor: Thomas M Wheeler, MD  more...
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Reference Range

The reference range for blood culture is no growth.

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Interpretation

True infection is almost always present if the culture is positive for one of the following organisms: [1, 2]

  • Streptococci (non-viridans)
  • Aerobic and facultative gram-negative rods [3]
  • Anaerobic cocci
  • Anaerobic gram-negative rods
  • Yeast

Negative growth does not rule out infection.

Suspect contamination if only one of several cultures is positive, if detection of bacterial growth is delayed (≥5 d), or if multiple organisms are isolated from one culture. [4]

Common contaminants include the following:

  • Staphylococcus epidermidis [5]
  • Bacillus species
  • Propionibacterium acnes
  • Corynebacterium species
  • Clostridium perfringens
  • Viridans Streptococcus
  • Candida tropicalis
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Collection and Panels

Specifics for collection and panels are as follows:

  • Specimen type - Whole blood
  • Container - Culture bottles (one aerobic and one anaerobic) for blood and green-top tube (heparin) for fungus and mycobacteria (if warranted by clinical suspicion)
  • Collection method - Venipuncture
  • Specimen volume - Adults: 10-20 mL per culture set; Pediatric patients: 1.0-3.0 mL

Other instructions are as follows:

  • Collect specimens as soon as possible after onset of chills or fever and before beginning antibiotic therapy.
  • Use aseptic technique (eg, clean venipuncture sites and culture vial tops with 2% chlorhexidine/70% isopropyl alcohol swabs before collection).
  • Draw 2-3 sets of cultures from separate sites at least 30-60 min apart (no more than 4 sets per 24-hour period).
  • Do not draw from IV catheter unless other sites unavailable.
  • Related tests - Complete blood count (CBC), urine culture, bacterial wound culture, gram stain, CSF analysis, fungal tests, susceptibility testing, sputum culture
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Background

Description

Blood cultures are used to identify microorganisms in the blood and to assist in guiding antimicrobial therapy. Common sources of bacteremia include the following: [6, 7]

  • Genitourinary tract
  • Respiratory tract
  • Abscesses
  • Surgical wounds
  • Biliary tract
  • Prosthetic cardiac valves

Indications/Applications

Indications for blood culture include symptoms of bacteremia or sepsis, such as the following:

  • Fever, chills
  • Rapid breathing and heart rate
  • Confusion
  • Severe hypotension
  • Decreased urine output
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