Blood cultures

Blood culture bottles are available in packs in blue bags which can be obtained from the laboratory during normal working hours – please ensure the ward areas are adequately stocked during the day.

Please store the packs at room temperature (15-30 C) away from direct sunlight or heat (i.e near radiators). Do not use out of date bottles, always check expiry dates on bottles before use and return any out of date bottles to the laboratory. After blood has been collected please send to the laboratory as soon as possible. To optimise the clinical utility of blood culture results, the interval between sample collection and being incubated in the laboratory should ideally be within 4 hours.

Bottles and procedure pack
A standard set of adult bottles consists of 2 bottles, a blue cap aerobic bottle and a purple capped anaerobic bottle
For Paediatric there is a single aerobic bottle for low-volume culture, (not more than 5 ml). These bottles have a yellow cap.
The laboratory provides the blood culture bottles in a blue bag which also contains a blood culture bottle adaptor cap, safety multifly needle, and antiseptic skin wipes and a sticker to record collection to be put in the patients notes.
Full instructions on taking the blood culture are printed on the bag, together with some of the clinical indications for collecting cultures on the reverse.

Patient ID stickers must not cover all of the bar code on the bottles, or cover the green detector pad on the bottom of the bottle. Please do not remove the peel off section of bar-code sticker from the bottle and place in patients notes as this is required in the laboratory, however it can be placed on the request form to assist in sample identification.

If possible take cultures before starting antibiotics, when the patient is already receiving antimicrobials, blood cultures should be collected just before the next dose is due when antimicrobial concentration in the blood is at its lowest.

Blood cultures should be taken once or twice during each clinical episode. A second set taken from a different site not only increases yield but also allows recognition of contamination, however it is recommended three times for endocarditis from different venepuncture sites. In most conditions other than endocarditis, bacteraemia is intermittent, given it is related to the fevers and rigors which occur 30-60 minutes after the entry of organisms into the blood stream, samples should be taken as soon as possible after a spike of fever.

Up to 20 ml of blood can be cultured per two-bottle set (minimum of 5ml in each bottle, maximum of 10mls). There is a direct relationship between blood volume and yield, false negatives may occur if inadequate blood culture volumes are submitted.

If the patient is difficult to bleed, a Paediatric bottle can be used which is designed for a low level of blood.

Taking the blood
Please see the current guide to taking a blood culture on the Trust Intranet under ” B” in Nursing procedures.
Label the bottles and send them to the laboratory with a Microbiology request card as soon as possible.
Do not refrigerate bottles, or warm them on radiators before transportation to the laboratory.
If the patient is “high risk” then ensure bottles and request card are labelled with danger of infection stickers.