Blood Cultures : Medical Assistants Class



  • A test to detect if an infection is present in the blood is a:

    blood culture

    Rationale: A blood culture is a test to find an infection in the blood. A blood culture can show if a bacteria or fungi are in the blood, which is not a normal occurrence. Blood cultures are typically ordered on patients that have signs of sepsis, such as fever, chills, nausea, and decreased urine output. Sepsis can be caused by a bacteria, yeast, or other toxic products that can cause harm to the body. It is essential to follow proper steps in collecting blood cultures to assure that the results are accurate, and that the patient received appropriate care.

  • The amount of blood that should be drawn for a blood culture is:

    40-60 ml per set

    Rationale: A blood culture specimen is drawn in a set of two bottles. When a blood culture is obtained, at least two sets should be drawn to make sure that the results are accurate. Each bottle should collect approximately 10ml of blood. Therefore, 40-60 ml of blood should be obtained each time blood cultures are obtained from a patient.

  • More than one set of blood cultures should be drawn:

    to prevent false positives

    Rationale: A false positive result of a blood culture typically is a result of skin contamination. If two or more blood culture sets are positive with the same bacteria, it is more likely that the microorganism found in the culture is causing the infection. If one set is positive and one set is negative, it could be an infection or contamination. The doctor will need to evaluate the person's clinical status and the type of microorganism found in order to determine the next step in care. If the blood culture sets are both negative, the probability that a person has sepsis caused by bacteria is low. If the patient continues to have symptoms of sepsis, such as a fever, additional testing may be required.

  • To determine what antibiotic will best treat an infection, the blood culture is used for:

    sensitivity testing

    Rationale: An antibiotic sensitivity test is done to help choose the antibiotic that will be most effective against a specific types of bacteria or fungus infecting a patient. Some types of bacteria or fungus are resistant to certain antibiotics because of differences in their genetic material. Infections caused by resistant bacteria or fungi are not cured by treatment with those antibiotics. Therefore, it is important to determine which antibiotics are most effective for certain infections in order to properly treat the patient.

  • Blood cultures should be drawn:

    prior to the start of antibiotics

    Rationale: Blood cultures should be drawn prior to the start of antibiotics when possible to help detect the cause of an infection. Collecting blood cultures prior to antibiotic administration offers the best hope of identifying the organism that has caused an infection in a patient. Failure to check blood cultures prior to antibiotic infusion may affect the growth of any blood borne bacteria and prevent a culture from becoming positive, even if the patient has a bacteria present.

  • When possible, blood cultures should drawn from:

    peripheral venous sites

    Rationale: Blood should be obtained from peripheral venous or arterial sites when possible. Obtaining blood cultures from central venous catheters, arterial lines and inguinal vessels increases the likelihood of obtaining a false positive blood culture. Blood for culture from IV catheters or the groin should never be performed when a peripheral site is available. This will decrease the chances of site contamination, and false positive results.

  • When the plastic flip lid is removed from a blood culture bottle, you should:

    clean the rubber stopper with an alcohol swab

    Rationale: Each bottle on a blood culture has a plastic lid, which covers a rubber stopper that serves as a cork for the top of a blood culture bottle. When a blood culture is collected, the needle penetrates the rubber stopper in order to collect the blood from the patient. Once the plastic lid is removed from the bottle prior to blood collection, the stopper should be cleansed with an alcohol swab. This is to decontaminate any bacteria that may have formed on the rubber stopper, and to assure an accurate blood culture result.

  • If blood cultures need collected at the same time as other laboratory tests, the blood cultures should be collected:


    Rationale: If a blood culture and other laboratory blood test need to be collected at the same time, the blood culture should always be the first bottles collected. This is to avoid contamination of the blood sample, and potentially causing a false positive result of the blood culture.

  • After a blood culture specimen is collected from a patient, the temperature that the bottles should be stored is:

    room temperature

    Rationale: Once a blood culture is obtained, the specimen should be stored at room temperature. Bacteria has an incubation time in which it takes to grow at room temperature, so heating or cooling an organism could alter the results of the culture. After a specimen is collected, it should be transported to the lab as soon as possible.

  • In order to prevent blood culture contamination, it is essential to:

    properly prepare the site

    Rationale: Proper site preparation and aseptic collection techniques are essential for blood culture collection. The ideal skin preparation for a blood culture is to cleanse the skin with Choloraprep, and let the area completely dry for 60 seconds prior to obtaining the specimen. If Chloraprep is not available, then the skin should be cleanse with an alcohol swab for 30 seconds, then let the area completely dry. The alcohol should be followed by a cleanse with iodine for another 60 seconds, then let the area completely dry again. Nothing should touch the site after it has been prepared for blood cultures, until after the specimen has been collected. Proper site preparation will decrease the risk of site contamination, and provide accurate results of a blood culture.


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