What Laboratory Tests Are Considered Blood Cultures
Blood cultures are laboratory tests that involve inoculating blood specimens into specialized culture bottles (aerobic and/or anaerobic) designed to detect bacteria, fungi, and yeasts in the bloodstream. 1
Standard Blood Culture Components
Blood cultures consist of the following elements:
- Aerobic blood culture bottles: Designed to detect aerobic and facultatively anaerobic organisms (bacteria and yeasts) 1
- Anaerobic blood culture bottles: Optimized for detection of anaerobic bacteria and may also detect facultatively anaerobic organisms, sometimes faster than aerobic bottles 1
- Blood culture sets: A complete set consists of all bottles inoculated from a single venipuncture or catheter draw, typically 2-3 bottles for adults (at least one aerobic and one anaerobic) 1
Specialized Blood Culture Types
Beyond standard aerobic/anaerobic bottles, several specialized blood culture systems exist for specific pathogens:
- Lysis-centrifugation tubes (Isolator): Used for enhanced recovery of Bartonella species, Legionella species, filamentous fungi, and dimorphic fungi 1
- Acid-fast bacilli (AFB) blood culture bottles: Specifically designed for detection of mycobacteria in blood 1
- Fungal-optimized bottles (e.g., MycoF/Lytic): Enhanced media for yeast detection, particularly when fungemia is strongly suspected 1
Rapid Molecular Blood Tests (Not Traditional Cultures)
While not technically "cultures," these direct-from-blood tests are increasingly used alongside traditional blood cultures:
- T2Candida Panel: FDA-cleared rapid molecular test detecting five Candida species directly from blood in 3-5 hours 1
- T2Bacteria Panel: FDA-cleared test detecting five bacterial species (E. faecium, S. aureus, K. pneumoniae, P. aeruginosa, E. coli) directly from blood 1
- Other rapid NAATs: Various nucleic acid amplification tests available outside the United States for direct pathogen detection from blood 1
Important caveat: These rapid molecular tests should only be used with concomitant standard blood cultures, never as standalone diagnostics, because blood cultures detect a wider spectrum of organisms and provide isolates for susceptibility testing 1, 2
What Is NOT Considered a Blood Culture
The following are distinct from blood cultures:
- Serology tests: Antibody detection for organisms like Bartonella, Coxiella burnetii, or Brucella species 1
- Peripheral blood smears: Direct microscopic examination for parasites or fungi 1
- Catheter tip cultures: These should never be submitted without accompanying blood cultures obtained by venipuncture 1
Proper Blood Culture Collection Standards
To optimize diagnostic yield, blood cultures require:
- Volume: 20-30 mL total blood per set in adults (10 mL per bottle), with age/weight-appropriate volumes for pediatric patients 1
- Number of sets: At least 2 sets (ideally 60 mL total blood) from different anatomical sites for adults with suspected bloodstream infection 1
- Timing: Sequential collection without time intervals between sets is acceptable; volume matters more than timing 1
Blood cultures remain the gold standard for detecting bloodstream infections, with modern automated continuous-monitoring systems providing positive results for most pathogens within 48 hours 1