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Blood Culture Mohammad Qtait RN, MSN
Bacteremia: the presence of bacteria in the blood. It may be transient, intermittent or continuous. • Blood culture: blood specimen submitted for culture of microorganisms. It enables the recovery of potential pathogens from patients suspected of having bacteremia or fungemia.
Blood culture set: the combination of blood culture bottles (one aerobic and one anaerobic) into which a single blood collection is inoculated. • Bloodstream Infection (BSI): an infection associated with bacteremia or fungemia.
Contaminant: a microorganism isolated from a blood culture that was introduced during specimen collection or processing and is not considered responsible for BSI (i.e., the isolates were not present in the patient’s blood when the blood was sampled for culture). • Contamination: presence of microorganisms in the bottle that entered during sampling but were not actually circulating in the patient’s bloodstream.
Sepsis: life-threatening organ dysfunction caused by a deregulated host response to infection.5 • Septicemia: clinical syndrome characterized by fever, chills, malaise, tachycardia, etc. when circulating bacteria multiply at a rate that exceeds removal by phagocytosis.
What is a blood culture? • A blood culture is a laboratory test in which blood, taken from the patient, is inoculated into bottles containing culture media to determine whether infection-causing microorganisms (bacteria or fungi) are present in the patient’s bloodstream.
Blood cultures are intended to: • Confirm the presence of microorganisms in the bloodstream • Identify the microbial etiology of the bloodstream infection • Help determine the source of infection (e.g., endocarditis) • Provide an organism for susceptibility testing and optimization of antimicrobial therapy
Why are blood cultures important? • used diagnostic tool for the detection of bacteremia and fungemia. • It is the most important way to diagnose the etiology of bloodstream infections and sepsis and has major implications for the treatment of those patients. • A positive blood culture also provides the etiologic agent for antimicrobial susceptibility testing, enabling optimization of antibiotic therapy.
When should a blood culture be performed? • Clinical symptoms in a patient which may lead to a suspicion of a bloodstream infection are: • undetermined fever (≥38°C) or hypothermia (≤36°C) • shock, chills, rigors • severe local infections (meningitis, endocarditis, pneumonia, pyelonephritis, intra-abdominal suppuration…). • abnormally raised heart rate • low or raised blood pressure • raised respiratory rate
Specimen Collection • Blood cultures should be drown prior to initiation of antimicrobial therapy, if more than one culture is ordered the specimens should be drawn separately at no less than 30 minutes apart to rule out the possibility of transient bacteremia by self-manipulation by the patient of mucous membrane in the mouth or by local irritation caused by scratching of the skin. • The numbers of bacteria are generally higher in the acute, initial stage than at a later stage of the disease, and small children usually have higher numbers of bacteria in the blood than adults. The number is also higher when the fever rises than when it is falling. • For patients expected to seed bacteria intermittently into the blood 80% of these are detected with the first culture and 99% within the three cultures.
Collection Time • Before starting antibiotics therapy if time permits, its generally recommended that the first two sets of blood cultures be taken one hour apart and the third set after 3-6 hours. • Obtaining the blood culture one half hour before a temperature spike is ideal because the highest concentration of organisms are circulating at that time, because the temperature spike is usually un predictable an educated guess must suffice in most cases when timing blood cultures. Volume Of Blood Culture Collected Acoording To Age Of Patients
Collection of Blood for Culturing • During blood culture collection all percussion should be taken to minimize the percentage of contaminated blood culture, to reduce the chance of contaminating organisms from the skin the vein puncture site should ideally be prepared as follows; • Wash with soap, rinse with sterile water or saline. • Apply 1-2 % tincture of iodine or povidone –iodine and allow drying for 1-2 minutes. • Remove the iodine with 70 % alcohol wash, if the site again be palpated after the iodine – alcohol preparation the finger must be disinfected or sterile gloves worn. • A tourniquet is applied to the upper arm above the vein puncture site to distend the anticubital veins.
Collection of Blood for Culturing • Remove Flip Caps from the tops of the selected culture bottles. Disinfect the septa of the bottles with alcohol or iodine preparation and allow to dry. • Perform venipuncture with syringe and collect the desired amount of blood. If the vein is missed a new needle should be used. • Transfer the recommended amount of blood into the culture bottles using aseptic technique if desired. First fill the aerobic bottle. Do not overfill the bottles! Any remaining blood may be used for additional tests. • Label the bottles according to the routine procedure. When using a sticker do not cover the tear-off section of the barcode label . Note: 1:5 to 1:10 blood/broth ratio is the appropriate ratio to achieved, this dilution minimizes the effects of microbial inhibitors present in blood and dilutes any antimicrobial agents.
Specimen processing • The bottle incubated for 24 hour before plating to enhance the growth of bacteria, aerobic bottle plate on blood agar, MacConky, and chocolate in CO2 incubator for 24 hour, anaerobic incubate anaerobically on blood agar for 48 hour, and the negative bottle should be reincubated and tested after 10 days before discarded as negative culture. If slow growing organisms are suspected as Brucella spp. its should be clearly indicated on the requisition form and the culture bottles should be further incubated for 2-4 weeks before being reported out as negative.
Blood bottles A set of blood culture: one aerobic bottle and one anaerobic bottle.
