Sterile blood cultures are performed to detect bacteremia, which indicates a serious infectious disease. The study is indicated to identify pathogenic microorganisms that are normally absent from the bloodstream: streptococcus, Pseudomonas aeruginosa, Staphylococcus aureus, enterobacteria, Klebsiella, yeast mushrooms. Possible infection with Staphylococcus epidermidis. It can only be detected by repeated testing. Microbiological cultures are important for the evaluation of patients with weakened immune systems. Patients with HIV infections may have Mycobacterium tuberculosis in their blood. To identify the type of bacteria, the properties of pathogens are studied: morphological, tinctorial (ability to react with dyes), cultural, biochemical, toxigenic, antigenic.
Normally, blood is sterile (does not contain bacteria). Sterility is maintained by factors of the immune system. The presence of bacteria in the blood (bacteremia) indicates an infectious disease. The study also allows us to evaluate the sensitivity of the isolated microflora to antibiotics.
Blood taken from a patient in the laboratory is sown on a special nutrient medium favorable for bacterial growth and left in a thermostat at a temperature of 37°C-38°C. After a few days, on the surface of the nutrient medium, the growth of bacteria becomes visible to the naked eye - colonies appear on it. By the appearance of the colonies, you can determine which bacterium caused the disease. If a bacterium is identified, it is re-cultured onto a new medium in a Petri dish, around the circumference of which paper disks soaked in a solution of various antibiotics are laid out. The dish is placed back in the thermostat and after a few days new colonies grow. If there is no growth around one of the discs, this will be an indication that the bacteria are killed or cannot grow in the presence of the antibiotic that is impregnated with the disc, and therefore, the administration of this antibacterial drug will be effective in the patient.
Normally, blood is sterile, that is, it does not contain bacteria.
Department of Health Voronezh region
BUZ VO "Voronezh Regional Clinical Hospital No. 1"
Blood test for sterility
at the present stage
Information and methodological letter for bacteriologists
Compiled by: chief freelance specialist in microbiological diagnostics
Department of Health of the Voronezh Region, head of the bacteriological laboratory
BUZ VOKB No. 1 E.V. Bondarenko
Bacteriologist BUZ VOKB No. 1 T.M. Paw
Blood is one of the most common samples of biomaterial studied in a bacteriological laboratory. Blood testing for sterility is the most important method laboratory research in patients with certain indications.
Main indications for blood culture:
Bacteria enter the blood through exogenous (for example, during injury) and endogenous (from the source of infection) routes.
Bacteremia: Presence of bacteria in the blood, confirmed by culture results
infection, such as infective endocarditis or septic thrombophlebitis.
Sepsis is a pathological process, which is based on the body’s reaction in the form of generalized (systemic) inflammation to an infection of various nature (bacterial, viral, fungal).
In the last decade, the world has seen an increase in cases of bacteremia and fungemia. This is due to the development of invasive medical interventions, an aging population, an increase in the number of organ transplants and bone marrow, an increase in the number of more virulent and difficult-to-treat microorganisms, and a more aggressive nosocomial infection.
Risk factors that contribute to the penetration of bacteria into the bloodstream and the development of bacteremia:
Blood culture is currently the “gold standard” in the diagnosis of septicemia
Principles of microbiological diagnostics
An accurate diagnosis is established only when pathogens are detected in the patients’ blood. Important condition- timely sample collection. For the analysis, blood is used directly from venous vessel. Collection of a sample from indwelling intravenous or intra-arterial catheters is allowed only in cases of suspected catheter-associated infection or the possibility of obtaining it by venipuncture.
Blood volume is one of the most significant factors in increasing the sensitivity of blood culture. The risk of accidental contamination of 1 individual blood sample is considered to be 3% (0.03).
Then the probability of accidental contamination of 2 samples at the same time is: 0.03 * 0.03 = 0.0009 = 0.09%. Therefore, it is more informative to study 2 or more samples, each with a volume of at least 10 ml.
Recommended number of blood samples taken depending on the suspected disease MU 4.2.2039-05 Technology for collecting and transporting biomaterials to microbiological laboratories :
1) Acute sepsis, meningitis, meningococcemia, osteomyelitis, arthritis, acute pneumonia, pyelonephritis 2 samples from two vessels or two sections of a blood vessel before starting antibacterial therapy
2) Fever unknown origin 4 first 2 samples from different blood vessels(two sections of the vessel), then after 24-36 hours another 2 samples
3) If you suspect the presence of endocarditis and sluggish sepsis: with an exacerbation, 2 samples from two vessels during the first 1 - 2 hours of rising body temperature (not at the peak of temperature!) before the start of therapy; in subacute and sluggish current first 3 samples with an interval of 15 minutes. and more. If all samples are negative, 3 more are collected on the second day after sowing.
4) in patients with endocarditis receiving antibiotics, 2 separate samples are collected over three days
5) For patients whose therapy includes antibiotics, 6 samples are collected within 48 hours; samples must be collected immediately before the next dose of the drug is administered
6) for fever of unknown origin, first 2 samples from different blood vessels, then after 24-36 hours 2 more samples
Minimum set of media for blood culture according to the provisions of Order 535:
“Double medium” - 1.7-2% nutrient agar slanted in a bottle (150 ml) and 150 ml of semi-liquid medium prepared in nutrient broth with the addition of 15 g of glucose and 0.15 g of agar.
“ Sterility control medium” is a standard thioglycollate medium to which 15-20 g of yeast extract and 4.25-5 g of agar per 1 liter are added; 0.001 g of resazurin is added to the medium as an indicator of anaerobiosis.
Necessary equipment for blood collection:
Technique for obtaining a blood sample. Blood samples for culture are collected by 2 people at the patient's bedside or in the treatment room.
Disinfect the area of skin above the vessel selected for puncture: treat the skin with a swab moistened with 70% ethyl alcohol, then with another swab moistened with 1 - 2% iodine solution or other disinfectant approved for use for these purposes in in the prescribed manner, in a circular motion, starting from the center, for 30 s; wait until the treated area dries. It is not allowed to palpate the vessel after treating the skin before inserting the needle;
When working with vials with dual media: use a sterile syringe to collect 10 ml of blood from adults, 5 ml from children; open the bottle over the flame of an alcohol lamp; add blood into the vial from a syringe, after removing the needle; burn the neck and stopper of the bottle in the flame of an alcohol lamp, close the bottle with the stopper; Carefully, so as not to soak the bottle cap, mix its contents in a circular motion.
Visual signs of blood culture growth during blood cultures
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Macroscopic |
Possible microorganisms |
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Streptococci, staphylococci, Listeria spp., clostridia, Bacillus spp. |
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Cloudiness |
Aerobic gram(-) bacilli, staphylococci, Bacteroides spp. |
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Gas formation |
Aerobic gram(-) rods, anaerobes |
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Film Formation |
Pseudomonas spp., Bacillus spp., yeast cells |
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Flake formation |
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Visible colonies (“smoky”) |
Staphylococci, streptococci |
Reasons for negative results:
Local infection ( protective forces the body keeps the infection in one place)
Irrelevant time of sampling (possibility of missing intermittent bacteremia)
The amount of material received is too small
Patient taking antibiotics
Identification of isolated bacteria during bacteremia:
Additional criteria in favor of the clinical significance of the isolate:
Rapid culture isolation - within the first 48 hours
Isolation of monoculture
Isolation of the same type of microorganism in different samples
Isolation of the same type of microorganism from blood and other loci
In addition to manual methods, there are automated blood culture methods that are more advanced and more sensitive. The most famous series of bacteriological analyzers for blood culture for sterility, - BDBACTEC.
The Bactec device is designed for rapid detection of bacteria and fungi in clinical blood samples. Blood samples are collected from patients and placed directly into the original culture bottles, after which - as quickly as possible - they are placed into the BD Bactec™ 9000 Series workstations. The presence of microorganisms in the blood is determined using highly sensitive fluorescent technology based on the indication of CO2 released into a nutrient medium by growing and intensively dividing microorganisms. With BD BACTEC 90% system positive results are detected in the first 24 hours of incubation, which allows timely initiation of empirical antibacterial therapy or make changes to the current scheme drug therapy. Timely bacteriological diagnosis of bacteremia significantly reduces the incidence of septic shock and increases the survival rate of patients.
Vials for blood culture are available in several types. The most commonly used are the following:
Designed for testing small blood volumes up to 3 ml, also contain latex particles
Vacuum blood collection is used using a butterfly needle blood collection system. The vacuum draws blood through the BD VacutainerTM needle directly from the vein into the BD VacutainerTM Tubes and BD BactecTM Vials and is immediately mixed with the culture medium.
Traditionally, blood sampling is carried out simultaneously into aerobic (BD BACTEC™ PLUS+ Aerobic/F) and anaerobic (BD BACTEC™ PLUS+ Anaerobic/F) vials. An alternative set consists of: a) an aerobic bottle and an additional aerobic one; b) anaerobic and/or Mycosis IC/F, and/or Myco F/Lytic bottles (both types of bottles are for the cultivation of fungal blood cultures).
Optimal blood volume for hemoculture
Simultaneously 20 -30 ml (10 ml per vial) of blood 2 or 3 times within 24 hours
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| STEP 2 |
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| STEP 3 |
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| STEP 4 |
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With proper blood sampling, contamination accounts for no more than 2-3% of all blood cultures. The use of BD VacutainerTM blood collection kits significantly reduces the contamination of cultures.
If there is growth of a microorganism in the vial, the analyzer notifies laboratory personnel using a light indication on the front panel of the device, as well as using a sound indication. Thus, there is no need to seed from all bottles; seeding is done specifically from the positive bottle.
Scope of research and micro-landscape during blood cultivation in bacteriological laboratories of medical institutions of the Voronezh region.
The total number of blood samples for sterility testing in the Voronezh region was 12,515. In 2013, this number was much lower: 8,406. The share of these tests by medical institutions is shown in the table:
The total number of positive cultures from blood samples in the region was 1245, which amounted to 9.95%, in 2013 808, which amounted to 9.6%.
Microlandscape of selected crops:
The following cultures were most often isolated from the blood: S. аureus - 165, coagulase-negative staphylococci - 639 (mostly S. epidermidis - 478), Enterococcus faecalis - 74, Pseudomonas sp - 59, Klebsiella - 54, E. coli-31, Enterococcus faecium 36. Among the fungi of the genus Candida, C. albicans and C. glabrata were most often isolated.
The following were isolated in small quantities: Enterobacter-18, Ps. aeruginosa 20, Acinetobacter 17, Streptococcus spp 20.
In quantities from 2 to 5, crops such as Str.viridans, Str. β-haemolyticus, Str pyogenes, Proteus mirabilis, Proteus vulgaris, Candida tropicalis, Candida krusei.
All bacteriological laboratories in the Voronezh region, with the exception of two, test blood for sterility manual methods. Bacteriological analyzers "Baktek" are available in the bacteriological laboratories of the Voronezh regional clinical hospital No. 1 and in the laboratory Perinatal Center 1k. As a result of the analysis of microbiological monitoring for 2011-2014, an increase in the number of microorganism cultures sown in these laboratories is noted. Before the use of hardware technology, the inoculation of microorganisms from the blood in 2010-2012 ranged from 6 to 10%, when studied using BD Bactec 9050 in 2013 - 24.7%, in 2014 - 26.9% in adult patients and newborns in 2013 17.5%, in 2014 - 20.3%.
Literature
1. “Manual of Medical Microbiology” edited by A.S. Labinskaya, N.N. Kostyukova, Moscow, 2013
2. “Methods of clinical laboratory research.” Reference manual edited by V.V. Menshikov. Volume 3 Clinical microbiology. M, 2009.
3. “Laboratory” magazine for doctors No. 5 2014
4. “Clinical microbiology” P.R. Marie, I.R. Shay, short guide, translated from English, Moscow, 2006
5. Clinical Microbiology and Antimicrobial Chemotherapy
2013, volume 15 (4).
Taking a blood test for sterility makes it possible to determine the presence in the body various types infectious processes. Read on to find out how this happens.
Blood is tested for sterility in cases where it is necessary to detect the presence of various types of pathogenic bacteria in the blood. At the same time, the analysis makes it possible to identify various processes occurring in the body. infectious diseases. This makes it possible to diagnose early stages the occurrence of tumors and other pathological processes.
A blood test for sterility is always prescribed for people who have weak immunity.
The main indications for blood testing include:
Sterility testing can be used as a preventive measure if there is a risk of developing infectious diseases. IN in this case bacterial culture will be carried out, allowing diagnosis to be made or, conversely, removed. This makes it possible to test the sensitivity of the infection to the antibiotics used for treatment or to develop a new course of therapeutic measures.
Blood culture itself for sterility is carried out in cases where it will be necessary to identify the presence of various types of bacteria in it, including pathogenic ones. Thanks to this it is possible to early stages detect the development of an infectious disease. A blood test makes it possible to determine the presence of microorganisms, the presence of which in healthy body very limited or completely unacceptable. These include: streptococci, Pseudomonas aeruginosa, Staphylococcus aureus, various types of enterobacteria and even yeast fungi.
A sterility test can show the possibility of contamination of such dangerous bacteria like, Staphylococcus epidermidis.
It is discovered after repeated testing has been carried out, with bacteriological culture. Such crops will have great value when studying samples taken from patients who have weakened immune system. This is especially important in cases where patients diagnosed with HIV infection are being examined. This is due to the fact that Mycobacterium tuberculosis is most often detected in them.
Any microflora that enters the blood or is detected in it as a result of a sterility test can cause or indicate the presence of infectious processes in the body. Moreover, with the help of blood, it will spread throughout the body, affecting organs and tissues. It can do more complex process, associated with identifying the root cause and place where the infection develops. The study allows not only to identify microorganisms, but also to establish the stage at which the disease is located.
A blood test for sterility, which is also called culture, or tank culture, allows you to detect the presence of pathogenic microflora.
Normally, the blood of a healthy adult is sterile. If, after taking an analysis, microflora was detected, this means that the person is seriously ill and needs adequate, complex treatment using antibiotics.
Using this method, it is determined whether a serious pathological process actually occurs, and based on the data obtained, adequate treatment methods are selected.
Indications for performing a bacteriological analysis to determine the sterility of blood are:
It is also recommended to do it if you need to install an internal catheter for a long time. In this case, the doctor also needs to make sure that there is no infection, and if there is one, identify its causative agent and eliminate it.
Sometimes the test is also prescribed for pregnant women, since during the period of bearing a child, a woman’s immunity decreases natural reasons, it becomes more vulnerable to infections of various kinds. The rules for preparing for the event and the execution algorithm are the same.
Note: There is no need to confuse microbiological testing of blood for sterility and blood culture. These are two different tests, the main difference of which is their scale. The first test shows whether bacteria are present in the patient's body at all. And blood culture reveals the characteristics of a particular type of microbe and allows you to monitor their activity.
The results of microbiological research change under the influence of internal and external factors, so it is important to minimize their impact through proper preparation.
Usually, a doctor or nurse always informs you how to properly prepare for a particular test, and in private clinics you can even get a special instruction.
But the main points proper preparation always the same:
If the patient violated the rules and kept silent about it, the analysis will not show a reliable picture and the testing will have to be repeated.
There are strict rules for collecting blood for bacterial culture, violation of which will lead to distorted results.
The sampling algorithm is as follows:
Attention! Taking blood for a similar test from a child infancy has its own characteristics. The difference is that the biomaterial is taken from the toe or heel in a volume not exceeding more than 5 ml.
Blood culture for sterility is carried out in several stages.
First, the doctor will sow the resulting biomaterial into a nutrient medium, then place the samples in a thermostat and keep them at 37-38 degrees for several days. On the second or third day, colonies of bacteria will be visible on the surface with the naked eye. Visually, the laboratory technician will be able to determine what type of bacteria they are.
After this, the microorganisms are re-seeded into a special device - a Petri dish. Paper discs soaked in various antibacterial drugs are placed around the circumference. The cup is placed again in the thermostat and kept for several more days.
This method establishes the sensitivity of microbes to antibiotics. The disk on the surface of which no colonies of microbes are found contains a medicine that can destroy pathogenic microflora. Based on the results obtained, an antibiogram is compiled, which will be used in further treatment.
A two-phase system for detecting blood cultures involves the use of a double nutrient medium. Typically this is a liquid medium, represented by broth, and a solid medium, represented by agar. The fact is that some microorganisms actively grow in a solid environment, while others spend most of their lives in a liquid substance. Therefore, to ensure rapid growth of bacteria, a two-phase medium is used.
In the video you can learn more about the analysis and the procedure for carrying it out:
As mentioned above, this analysis will show the presence of pathogenic microflora in the biomaterial and its type.
Specifically, it detects pathogenic microorganisms of the following groups:
Even in a private laboratory equipped with all the necessary modern equipment, the analysis takes at least 10 days. A positive or negative result will be known within two to three days, but in order to accurately identify the types of pathogenic microflora and its activity, you will need to alternately introduce various reagents and components and wait for a reaction.
Such periods are necessary so that the bacteria have time to grow. The rate of germination of pathogenic microorganisms depends largely on their type. If the patient has severe symptoms of acute inflammatory process, the doctor will prescribe antibacterial drugs after blood sampling wide range actions. But truly effective, adequate treatment can only be selected after the full results indicating the causative agent of infection.
Deciphering and making a final diagnosis is carried out exclusively by a doctor.
The cost of the study is determined based on the level of the clinic and laboratory in which the analysis is performed. IN district clinic by doctor's direction this procedure is performed completely free of charge, provided that the local laboratory has the necessary tools and materials.
The cost in private clinics will depend on the level medical institution and the research techniques used (what media are used). Average price for this analysis in the Russian Federation is 500 – 600 rubles. In the capital and large cities, the cost can increase to 700 rubles.
It is recommended to carry out a detailed blood test for sterility if an infection of bacterial origin is suspected; this is not a mandatory study.
Using the analysis, the presence or absence of pathogenic microorganisms in human blood is first determined, then their type and activity. Blood is also donated to check the patient’s sensitivity to certain antibacterial drugs and compose effective scheme treatment.
The reliability of the results, subject to compliance with all the rules of preparation, sampling and laboratory testing, is 95%.
Not every patient knows why doctors in clinics write out referrals for various examinations, including blood tests for sterility. Doctors assure that this testing is prescribed to identify bacteremia in a patient, which indicates the presence of pathogenic processes in the body.
To get a reliable result and the opportunity to start competent treatment, the patient needs to know the rules of blood sampling and strictly follow some recommendations for several days.
Blood culture for sterility - what is it and why is it called that? This examination is one of the most important, since it gives doctors the opportunity to identify the presence of microorganisms in the blood that indicate the development various pathologies, internal inflammatory process.
U healthy person blood and other body fluids must be sterile, and if testing is negative, this indicates the presence of some kind of disease. To determine a violation of sterility, hematological culture on various nutrient media is most often prescribed.
The main purpose of the analysis is to identify the presence of harmful microorganisms that provoke the inflammatory process.
The diagnostician may prescribe the patient to donate blood for microbiological testing in the following cases:
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The absolute indication for testing is the presence of artificial myocardial valves. To obtain a reliable analysis result, you will have to wait at least 10 days, since the germination of pathogenic microorganisms will take several days.
Experts warn that the speed of this process depends on the type of pathogen. It is worth noting that after collecting biomaterial, many patients are prescribed antibiotics (based on the presenting symptoms), but choosing a more competent and optimal treatment regimen is possible only after receiving hemotest data.
In most cases, bacterial culture for sterility is prescribed for detection in the blood harmful bacteria and microbes such as:
This study is necessary for patients who have reduced body defenses, as well as for people suffering from dangerous pathologies, such as HIV, tuberculosis, acute infectious diseases. In addition, testing is often prescribed if doctors cannot decide on the optimal treatment regimen.
Testing for the presence of pathogenic microorganisms allows us to determine the presence of the following pathologies:
To detect the type of blood culture, a thorough analysis of the suspected pathogen is required. If the study shows its presence in the body, doctors will need to find out how serious a danger the detected microbes pose to various systems and internal organs.
Only after receiving the necessary information will doctors be able to prescribe optimal therapy for the patient.
If a person needs to conduct such a study, it is better to make an appointment at a private diagnostic center. The main condition is the presence of a laboratory for microbiological research there.
As practice shows, in such institutions the decoding of results is carried out in the shortest possible time . The cost of the procedure may vary depending on the type of clinic, but usually the price of testing varies between 400-700 rubles.
Since bacterial culture is a microbiological study, the reliability of the result may be affected by internal and external factors.
To prevent a false result, the patient needs to perform certain preparations:
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If the patient ignores the rules, the likelihood of receiving an incorrect test result increases several times, which may lead to the need for secondary testing.
The algorithm of actions is very simple, but the most important moment is to comply with the fence technique. The biomaterial must be taken strictly from the vein of the elbow. The physician must ensure that no external contaminants enter the bloodstream.
To prevent damage to the biomaterial, blood is drawn using a disposable sterile needle.
Before proceeding with it, the area of the epidermis must be treated antiseptic solution. In most cases, about 10 ml of biomaterial is taken from the patient, after which it is placed in a bottle with a nutrient medium that prevents changes in the structure of the blood.
To reduce the risk of infection, blood from a syringe is poured into a bottle located above the burner flame. After these steps, the vial is sealed with a tight lid and placed in a special container until further research is carried out.
In the rarest cases, the patient is injected with adrenaline before blood sampling, since the substance increases the accuracy of the analysis and helps to identify the maximum number of pathogens.
In a child, blood manipulation is carried out differently. Biomaterial is removed only from the toe or heel. For bacterial culture, no more than 5 ml of blood is taken from children for sterility testing.
How long it takes to prepare an analysis is of interest to all patients. If the procedure was carried out in a modern diagnostic center, the first data can be obtained within a couple of days, but the form with the final results will be given to the patient no earlier than after 10 days. This is due to the fact that the blood will be subjected to various studies, and various reagents and substances will be added to the biomaterial.
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Doctors assure that this testing is guaranteed to provide the correct result and the ability to assess the general condition of the patient and identify the presence of certain pathologies.
Inaccurate data can only appear if the patient ignored medical recommendations and preparation rules before donating the biomaterial.
If all requirements are met, the probability that a person will receive reliable information about his condition reaches 95%.
Today, sterility testing is indispensable, as it makes it possible to evaluate blood cultures and conduct research using various pathogenic organisms.
In addition, during the study, you can find out how the body reacts to the consumption of certain drugs, thanks to which doctors will be able to choose the best treatment regimen.
If a person has a periodic increase in body temperature without visible reasons, you should not hesitate to make an appointment with a specialist, who, after conducting a physiological examination and taking an anamnesis, will issue a referral for further diagnostics.
We cannot exclude the possibility that one of the first on the list will be a blood test for sterility, since based on this testing it is possible to draw conclusions about general condition patient and prescribe a competent treatment regimen.
