Going to the hospital for medical treatment, blood tests are the most common measure. There is a type of test that requires a large amount of blood to be drawn, sometimes multiple times. This test item is called "blood culture". Many patients are not very familiar with this examination. Below, we will explain the popular science knowledge in this regard.
What is blood culture?
Blood culture is an artificial cultivation method that involves inoculating fresh blood samples into a specialized liquid culture medium for blood culture, placing them in an incubator at 35 ℃~37 ℃, allowing pathogenic microorganisms to grow and reproduce, and identifying them to determine the pathogen.
Why is blood culture recommended for testing?
Blood culture is commonly used for the etiological diagnosis of bacteremia and mycosis, as well as for the auxiliary diagnosis of patients with unexplained long-term fever. According to work statistics, the positive rate of blood culture is 8% to 15%. The detection of microorganisms in the blood of patients has important clinical significance for the diagnosis, treatment and prognosis of infectious diseases.
When is the best time to collect blood when suspecting bloodstream infection?
1. Collect blood as much as possible within 0.5-1 hour before the onset of chills and peak fever in patients; It can also be done 1 hour after shivering or fever;
2. Collect blood from patients before receiving antibiotic treatment;
3. If the patient has already been treated with antibiotics, blood should be collected and cultured before the next medication;
What are the requirements for blood culture collection?
According to China's blood culture collection standards:
1. Adults are usually recommended to collect 2-3 sets of blood culture specimens (each set includes one aerobic bottle and one anaerobic bottle) in different locations within a short period of time (usually within 1 hour), totaling 4-6 bottles, with 8-10ml of blood collected from each bottle.
2. Infants and young children only need to collect 2 specialized culture bottles for children at different locations in a short period of time, with each bottle collecting 1-3ml of blood volume.
When there is suspicion of infective endocarditis or other intravascular infections (catheter-related) bacteremia and mycosis, blood samples should be collected at intervals (e.g. every 1-2 hours), with 2 to 3 sets (2 bottles/set) of blood cultures, and 8-10ml of blood should be collected from each bottle.
Why use multi site blood collection and collect multiple sets of blood cultures?
When collecting blood culture samples, nurses may perform multi site blood collection on patients instead of collecting all blood samples in one shot, which can ensure that doctors make correct interpretations of positive blood culture results and confirm the true pathogenic bacteria. This is the need for scientific blood collection.
At the same time, due to the fact that bacteria and fungi are uniformly present in the blood in most cases, the sensitivity of a single blood culture test is limited. Therefore, it is necessary to take two or more pairs of blood cultures, and the contaminating bacteria usually only appear in one blood culture bottle. For true bloodstream infections, multiple blood culture bottles are positive. According to statistics, the cumulative detection rate of blood culture combinations increases with the number of sampling times. The detection rate of one pair is 73.2%, the detection rate of two pairs is 93.9%, and the detection rate of three pairs is 96.9%.
What should be paid attention to in blood culture collection?
During the blood culture collection process, standard and strict aseptic procedures must be adopted;
2. Ensure sufficient blood collection volume;
3. Pay attention to the blood collection sequence: If using a syringe or needle for blood collection, first inoculate an anaerobic bottle to prevent air from entering; If using a butterfly needle for blood collection, the aerobic bottle should be inoculated first to prevent the air in the device from being transferred to the anaerobic bottle; If the amount of blood extracted is less than the recommended amount, sufficient blood should be inoculated into aerobic bottles first, and the remaining blood should be inoculated into anaerobic bottles.
How many milliliters of blood is collected each time?
1. Children: Collect sufficient blood volume based on age and weight, not exceeding 1% of the total blood volume of the child;
2. Newborns: ≥ 0.5ml/bottle;
3. Infants and young children (1-36 months): ≥ 1.0ml/bottle; (≥ 36 months): ≥ 4.0ml/bottle;
4. Adults: 10ml per bottle, 20ml per set, two sets totaling 40ml. How long can we know the blood culture results?
The automatic blood culture system reports over 95% of positive results within 48 hours of starting the test, but negative results need to be cultured for 5 days before the report can be released. This is done to maximize the detection of pathogenic bacteria in the blood, such as Brucella, which usually takes 4-5 days to report positive.
What types of specimens can blood culture cultivate?
In addition to blood, blood culture can also detect many sterile body fluid specimens, such as cerebrospinal fluid, pleural effusion, joint effusion, etc.