Blood Culture Collection and Transportation Guide:
A. Blood cultures are indicated for a sudden relative increase in patient’s pulse rate, temperature, change in sensorium or blood pressure, chills or any prolonged or intermittent fever in association with heart murmur
B. In general, if any time bacterial, fungal, or mycobacterial sepsis is suspected.
What is a Blood Culture?
A blood culture is a laboratory test in which blood is injected into bottles with culture media to determine whether microorganisms have invaded the patient’s bloodstream. Blood cultures are ordered as a set, which consists of 2 bottles (1 aerobic bottle & 1 anaerobic bottle).
The Contaminated Blood Culture
If the skin is not adequately cleansed before drawing blood for culture, bacteria on the skin will be injected into the bottle producing a false positive blood culture.
It is sometimes difficult for the physician to determine whether the bacteria growing in the blood culture is a real pathogen causing bloodstream infection or whether bacteria on the skin have contaminated the culture. This can lead to excess use of antibiotics and prolongation of hospital stay.
Human skin has a bacterial concentration between 103 and 106 CFU/mL, on the forearm and groin, respectively. The most common source of contamination is the process of phlebotomy and inoculation of blood culture bottles. The primary agents for skin disinfection is chlorhexidine
Principles for Collection:
After placing a tourniquet on the patient’s arm, select a suitable vein.
- Cleanse the area with the 2% iodine followed by 70% alcohol, in circular motion from the centre to outside and allow it to dry for at least 60 seconds.
- During this period, prepare lids of blood culture bottles by cleaning with iodine and/or alcohol.
Now without touching the site of the venipuncture with the fingers, draw 10-20mL of blood into a sterile syringe. If other blood tests are required than first take the blood culture specimen from aseptic site.
Inoculate culture bottles without changing needles. Gently invert the bottles several times to insure thorough mixture of the contents.
Points That Should be Communicated to the Clinicians Before Blood Culture Collection
Collect blood during the early stages of disease, during peak of fever since the number of bacteria in blood is higher in the acute and early stages of disease.
- Blood cultures should be sent prior to antibiotic administration.
Three blood cultures sets are recommended at one hour intervals to obtain 99% positivity.
Small children usually have higher number of bacteria in their blood as compared to adults and hence lesser volume (3-8 mL) is required for culture.
Volume of blood to be collected for routine blood cultures:
Adults: 20 ml of blood should be collected by syringe and equally divided between each BacT Alert bottle. If this amount cannot be obtained, a lesser amount may be used and equally divided between the bottles (Bactec Plus + Aerobic and Bactec anaerobic / Bactec Peds plus )
If 5 ml or less is collected, place the entire amount in the aerobic bottle. Notify the laboratory if this occurs by writing amount collected on laboratory requisition form.
Transport to Microbiology Lab:
1. Transport immediately (within two to four hours) to the microbiology laboratory
2. All blood culture bottles should be handled properly to avoid breakage and spills.
3. All blood culture specimens should be taken as potentially hazardous.
4. Minimize direct handling of specimens in transit from the patient to the laboratory whenever possible.
5. If delayed, leave at room temperature. Do not refrigerate.
Blood cultures are usually incubated for five days. Some organisms such as Brucella spp.and certain streptococci may take longer than five days to grow then they are incubated for 21 days.
Preliminary reports are available at 24 hours and 48 hours and final report after six
Positive results are always phoned. Fungal cultures are held for 28 days
Dr Summiya Nizamuddin
Consultant Medical Microbiologist
Shaukat Khanum Memorial Cancer Hospital and Research Centre (SKMCH&RC)
Updated June 2018