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Blood culture

Blood culture is the culture of micro-organisms from blood for the laboratory diagnosis of bacteraemia, infective endocarditis and other conditions associated with pyrexia of unknown origin.

Mortality due to bacteraemia is related to the type of organism isolated and the nature of any underlying disease. Early positive results from a blood culture can provide valuable diagnostic information on which appropriate antimicrobial therapy can be based.

Specimen requirements

Samples should be transported to the laboratory as soon as possible, ideally within four hours of collection. These are urgent samples, and if transport will be delayed, do not store in a refrigerator.

Ideally blood cultures should be taken before the start of any antimicrobial therapy and as soon as possible after a spike of fever. The recommended specimen volume of blood is:

  • Bactec Plus Aerobic/F bottle: 5-10 ml
  • Bactec Lytic 10 Anaerobic/F bottle: 5-10 ml
  • Bactec PEDS Plus/F bottle: 1-3 ml

It is important that the sender makes clear to the laboratory the site of collection of the blood sample and also if the sample is from a high-risk patient.

See also: High-risk specimens

Samples other than blood may be received in Bactec bottles, e.g.:

  • CAPD fluids
  • homografts
  • joint aspirates
  • pleural fluids
  • CSF.

Laboratory turnaround time

Please see Turnaround times

Laboratory method

Blood culture bottles are usually received as a pair; one aerobic and one anaerobic bottle, making a blood culture set.

More than one set may be collected from a patient. In the case of neonates and children a single PEDS bottle is routine.

The bottles, once received in the laboratory, are placed onto the BD Bactec FX where they are monitored for bacterial growth. Any that flag as positive, i.e. growth is suspected, are subbed onto non-selective media and a Gram stain performed.

The Gram stain result is vital in informing the clinicians of the potential nature of the patients' infection; antimicrobial treatment can then be confirmed or adjusted as soon as possible.

Where to find results of these tests

  • All results are returned electronically where possible (EPR, SunquestICE).
  • Some results may be phoned to clinicians and GPs.
  • Results are never given directly to patients by the laboratory staff.

Further information and contact details

For further information please email:

Confidential patient information should only be sent from accounts.

Microbiology Laboratory Users Manual (pdf, 684 KB)