Blood Culture

Last updated 30th July 2021

Blood culture is the gold standard for diagnosing septicaemia and is an integral part of the Sepsis 6 bundle. They provide clinicians and microbiologists with the information they need to progress to targeted antibiotic therapy.

Indications

Abnormal core temperature <36°C or >38°C
Focal signs of infection
Tachycardia (>90), blood pressure (low or raised), elevated respiratory rate (>20)
Chills/rigors
Abnormal white cell count (<4 or >12)
New or worsening confusion
Severe Inflammatory Response Syndrome (SIRS) – two or more criteria met
NB Only take blood cultures when there is a clinical indication to do so and not as routine.

Timing

Blood cultures should be taken at the earliest possible time following clinical suspicion of sepsis.
If you are collecting other samples, collect blood cultures first
Blood cultures should always be obtained before administration of antibiotic therapy but without unduly delaying treatment in emergencies.
Specimens can still be collected after antibiotics have been commenced but this reduces the probability of identifying the causative organism.

Skin Asepsis and Technique

Aseptic collection of blood from the patient is imperative to avoid contamination of the specimens with skin flora.
NHS D&G have introduced a new system for blood culture collection using the BD Vacutainer® Push Button™ Safer Butterfly Blood Collection Set with Pre-Attached Holder.
Ideally cultures should not be taken from a peripheral venous cannula, even if newly inserted but it is understandably difficult in emergency scenarios. In these cases, please take a second set of cultures as soon as a peripheral stab is possible
Avoid venepuncture from:
- the upper limb on the same side as a previous mastectomy
- fistulas
- infected/excoriated skin
- a vein immediately above a peripheral cannula
Take two sets of cultures, always making a fresh stab for each specimen – the interval between cultures does not have significant influence.
In suspected endocarditis, a minimum of three sets (native valve) or up to 6 sets (prosthetic valve) should be collected over 24 hours or over 1 hour if critically unwell. Please make separate stabs for each set.

Central Venous Catheters

Take one set of cultures from the line plus a separate peripheral stab.
In the absence of a suitable peripheral venous site, an arterial blood site can be considered a valid alternative, because arterial blood has been shown to perform similar to venous blood in terms of contamination and sensitivity.
Cultures from each lumen are not necessary in the case of a CVC

Hickman Line

Take one set of cultures from each lumen, labelled appropriately along with a peripheral sample.