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Blood Culture Is More Important Than Imagination
Nov 24, 2018

What is bacteremia? What is the clinical significance of blood culture?

The immune system is an important system for the body to perform immune response and immune function. It is the most effective weapon for preventing the invasion of pathogens. It can detect and remove foreign bodies and foreign pathogenic microorganisms. When microorganisms invade the blood and rapidly multiply beyond the immune system, they form blood. Symptoms or fungalemia.

Bacteremia is one of the most common clinical critical illnesses, and the mortality rate is as high as 20%-50%. The detection of microorganisms in the blood of patients has important clinical significance for the diagnosis, treatment and prognosis of infectious diseases.

Blood culture is the most important means of diagnosing bacteremia. Bacteria isolated from blood may be the cause of sepsis, which provides an important basis for the diagnosis of the cause, and can further provide a basis for correct antibiotic treatment; blood culture positive also indicates The body limits infection and the failure of a particular site to act or the spread of local infections.

Blood culture related items: bacteremia, fungal blood culture, mycobacterial culture, catheter-related bloodstream infection, infective endocarditis.

What symptoms do blood culture?

Fever (>38 ° C), hypothermia (< 36 ° C), leukocytosis (> 10.000 / μl) neutropenia (< 1.000 / μl), hypotension, local infections: pneumonia, urinary tract infection, meningitis Children with sudden onset of mental retardation or the elderly, frail, mentally disordered, sudden decline in weight, renal insufficiency, unexplained leukocytosis and altered mental status, immunocompromised patients, CRP, PCT.

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Influencing factors:

At present, the positive rate of blood culture is low. According to relevant statistics, the positive rate of blood culture in China is about 10%-18%, and the positive rate is related to many factors.

1, skin preparation and pollution prevention (disinfection, blood culture acceptable pollution rate is ≤ 3%)

2. The timing of specimen collection (the time when bacteria enter the bloodstream is 1 hour before chills and fever)

3, blood collection (adults 20-30ml, for infants and young children, blood collection does not exceed 1% of the total blood volume of the patient, the increase in blood collection will increase the positive rate)

4. Distribution in aerobic and anaerobic bottles (a blood culture should include 1 aerobic and 1 anaerobic bottle)

5. Specimen transport (should be sent to the laboratory immediately after the collection is completed. The blood culture bottle after inoculation should not be refrigerated or frozen. Any delay in feeding the automatic continuous monitoring of the blood culture instrument will delay or prevent the detection of bacterial growth)


How many sets should be taken for blood culture? How many bottles per set?

CLSI requires 2-3 sets of specimens to be collected each time, each set should include an aerobic culture flask, an anaerobic culture flask

Adult patients can not only take 1 bottle of blood culture specimens. The results of insufficient blood collection and only one set of blood culture are difficult to explain correctly.


Why does a blood culture choose a combination of aerobic and anaerobic?


Studies have shown that Staphylococcus aureus, a combination of aerobic bottles and anaerobic bottles, some bacteria and bacteria in Enterobacteriaceae are more than a pair of aerobic bottles.

Report time is advanced:

Positive time

  9% of aerobic bottles report results 1 day earlier than anaerobic bottles

  5% of anaerobic bottles report results 1 day earlier than aerobic bottles

Therefore, only aerobic bacteria can be used for anaerobic culture, 19% of the strains can not be found, and 5% of the blood cultures are delayed by 1 day.

If the blood culture is only used for aerobic bottle culture, the missed test will not only strictly anaerobic bacteria, but also affect the isolation rate of facultative anaerobic bacteria and the time to report positive results.


How much blood should the patient collect?

That is, chilling - 20 ml of blood collected between warming, divided into two bottles, each dispensing 10ml, when the blood collection is less than 20ml, should first be injected into the aerobic bottle, so that the first to meet the aerobic bottle of blood can better separate the fungus, Pseudomonas aeruginosa, Stenotrophomonas maltophilia.


How should children's blood culture be collected?


Children have very few anaerobic infections. It is recommended to use only children's bottles.

Anaerobic culture is only considered for special high-risk children

For infants and young children, the amount of blood collected does not exceed 1% of the total blood volume of the patient.

<1 month: ≥ 0.5 mL

January – 36 months: ≥ 1.0 mL

≥ 36 months: ≥ 4.0 mL

Reason: The blood bacteria content of adult bacteremia is usually ≤10CFU/ml, most of them are less than 1CFU/ml; children can reach 100~1000CFU/ml

    Children's bottle for automated instruments: recommended blood volume 1-4ml / bottle

Neonatal sepsis

The lowest blood volume is uncertain, and a blood volume of 0.75-1.0 ml is usually recommended.

The literature confirms that only 10%-15% of sepsis in a blood culture can not be detected.

Even if blood culture is negative, sepsis can still be suspected according to clinical symptoms


How to disinfect skin and blood culture bottles?

   US CLSI recommended skin disinfection method: first determine the venipuncture point, preferably 70% isopropyl alcohol disinfection and to be dried, and then disinfected with the main disinfectant (chlorhexidine, iodine, iodophor) and dry, so that it works enough Time, the entire process requires strict aseptic operation

Blood culture bottle disinfection method:

   Discard the plastic cap on the top of the bottle and sterilize the top rubber stopper with 75% ethanol. Wait 60 seconds.

What is the interval between blood collections?

   The interval between each blood culture should not exceed 30 minutes, because the reticuloendothelial system can be cleared within 15 to 30 minutes for transient bacteremia and intermittent bacteremia (CLSI requires that each blood culture should be obtained at the same time, or May be short)


The blood specimen is a VIP specimen of the microbiology room, which is of great help to clinical treatment. However, the blood culture specimens account for a very low amount of microbial specimens, which should be paid enough attention to us so that we can be responsible for the clinical and patient.


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