Blood cultures

Blood cultures should always be taken when a bloodstream infection is suspected and ideally before antibiotics are given.

Clinical symptoms in a patient which may lead to a suspicion of a bloodstream infection are:

• pyrexia or hypothermia (absence of fever does not exclude blood stream infection)
• shock, chills, rigors
• severe local infections (meningitis, endocarditis, pneumonia, pyelonephritis, discitis)
• abnormally raised heart rate
• low or raised blood pressure
• raised respiratory rate

• In adults, it is recommended that a minimum of 2 sets of blood cultures (4 bottles in total) per episode. Ideally from different venepuncture sites
• Each blood culture bottle should be filled with 10ml of blood, for each ml of blood there is an expected 3% increase in yield of pathogen.
• A minimum of 3 sets is recommended for suspected infective endocarditis or candidemia.
• Lines should only be sampled when there is suspicion of possible line infection, and a peripheral blood culture should be taken at the same time.

1. Confirm the patient’s identity and gather all required materials before beginning the collection process. Do not use blood culture bottles beyond their expiration date, or bottles which show signs of damage.
2. Wash hands with soap and water then dry or apply an alcohol hand rub or another recognized effective hand rub solution. Remove the plastic “flip-cap” from the blood culture bottles and disinfect the septum using an appropriate and recognized effective disinfectant, containing 70% isopropyl alcohol. Use a fresh swab for each bottle. Allow bottle tops to dry.
3. If skin is visibly soiled, clean with soap and water. Apply a disposable tourniquet and palpate for a vein. Apply clean examination gloves and cleanse the skin using an appropriate disinfectant, such as chlorhexidine in 70% isopropyl alcohol. Allow to dry.
4. Collection method:
   1. If using a needle and syringe: Attach the needle to a syringe. To prevent contaminating the puncture site, do not re-palpate the prepared vein before inserting the needle. Insert the needle into the prepared vein. Collect the sample. Transfer the blood into the culture bottles, starting with the anaerobic bottle. Hold the bottle upright and use the graduation lines to accurately gauge sample volume. Add 10 ml of blood per adult bottle. Once the anaerobic bottle has been inoculated, repeat the procedure for the aerobic bottle.
   2. If using winged blood collection system: Attach a winged blood collection set to a collection adapter cap. To prevent contaminating the puncture site, do not re-palpate the prepared vein before inserting the needle. Insert the needle into the prepared vein. Place the adapter cap over the aerobic bottle and press straight down to pierce the septum. Hold the bottle upright, below the level of the draw site, and use the graduation lines to accurately gauge sample volume. Add 10 ml of blood per adult bottle. Once the aerobic bottle has been inoculated, remove the adapter cap and repeat the procedure for the anaerobic bottle.
5. Discard the needle and syringe or winged collection system into a sharps container and cover the puncture site with an appropriate dressing. Remove gloves and wash hands before recording the procedure, including indication for culture, time, site of venipuncture, and any complications. Ensure additional labels are placed in the space provided on the bottle label and do not cover the bottle barcodes, and that the tear-off barcode labels are not removed.

Blood culture bottle should be labelled as follows:

Blood cultures should then be transported to the laboratory urgently, via the POD where available.

Blood cultures are incubated for a total of 5 days from receipt in the laboratory. Most significant pathogens will flag positive within 48hrs (see table below for local data on time to positivity for common organisms). Positive results will be immediately updated on clinical portal and all significant results will be called to ward staff.

Common blood culture contaminants include coagulase negative staphylococci, Micrococcus luteus, Corynebacterium spp (‘diptheroids’), Cutibacterium acnes and Bacillus spp. These organisms rarely cause infection and are of doubtful significance. Where prosthetic material is present eg CVC and yielded from multiple cultures the microbiologist will advise on treatment options.

When a significant pathogen is grown from blood cultures, the microbiologist will contact clinical staff and discuss treatment options. In general, a minimum duration of 7 days is required with 14 days recommended for some organisms. Additionally, if an uncontrolled focus of infection is present longer courses will be required. Treatment of blood stream infections should be with intravenous antibiotics or highly orally bioavailable agents. Beta-lactam agents (eg amoxicillin/co-amoxiclav) are NOT considered highly orally bioavailable and would not be recommended as oral treatment options for bacteraemia. Final susceptibility results are usually available between 24 and 48hrs from flagging positive.

Staphylococcus Aureus Bacteraemia (SAB) Guidelines on Management in Adults (188)

Invasive Candidiasis in Non Haemato Oncology Adult Patients (173)