Culture, Bacterial, Blood

Culture, Bacterial, Blood

Synonym/acronym: N/A.

Common use

To identify pathogenic bacterial organisms in the blood as an indicator for appropriate therapeutic interventions for sepsis.

Specimen

Whole blood collected in bottles containing standard aerobic and anaerobic culture media; 10 to 20 mL for adult patients or 1 to 5 mL for pediatric patients.

Normal findings

(Method: Growth of organisms in standard culture media identified by radiometric or infrared automation, by manual reading of subculture, or PCR.) Negative: no growth of pathogens.

Description

Pathogens can enter the bloodstream from soft-tissue infection sites, contaminated IV lines, or invasive procedures (e.g., surgery, tooth extraction, cystoscopy). Blood cultures are collected whenever bacteremia (bacterial infection of the blood) or septicemia (a condition of systemic infection caused by pathogenic organisms or their toxins) is suspected. Although mild bacteremia is found in many infectious diseases, a persistent, continuous, or recurrent bacteremia indicates a more serious condition that may require immediate treatment. Early detection of pathogens in the blood may aid in making clinical and etiological diagnoses.

Blood cultures can detect the presence of bacteria and fungi. Organisms can be classified in a number of ways; blood culture findings use oxygen requirements to categorize findings into one of two groups. Blood culture begins with the introduction of a blood specimen into 2 types of culture medium. The medium is designed to promote the growth of organisms; one group of organisms require oxygen (aerobic) and the other either requires sparing amounts to no oxygen at all (anaerobic). A blood culture may also be done with an antimicrobial removal device (ARD) if antibiotic therapy is initiated prior to specimen collection. This involves transferring some of the blood sample into a special vial containing absorbent resins that remove antibiotics from the sample before the culture is performed.

Traditional automated culture methods entail incubation of innoculated culture containers for a specific length of time, at a specific temperature, and under other conditions suitable for growth. If organisms are present they will produce carbon dioxide as they metabolize the nutrients in the culture media. The presence of carbon dioxide in the culture is detected when the culture bottles are “read” by an instrument at specified intervals over a period of time. There are a number of automated blood culture systems with sophisticated computerized algorithms. The complex software allows for frequent monitoring of growth throughout the day and rapid interpretation of culture findings. With these systems as soon as a positive culture is detected, usually within 24–72 hr, the bottle can be removed from the system and a gram stain performed to provide a preliminary identification of the bacteria present. This preliminary report provides an opportunity for the HCP to initiate therapy. A sample from the positive blood culture bottle is then subcultured on the appropriate plated media for growth, isolation, and positive identification of the organism. The plated organisms are also used for sensitivity testing, if indicated. Sensitivity testing identifies the antibiotics to which the organisms are susceptible to ensure an effective treatment plan and can take several days. Negative cultures are generally removed from the automated culture system after 5 days and finalized as having “No Growth.” The subspecialty of microbiology has been revolutionized by molecular diagnostics. Molecular diagnostics involves the identification of specific sequences of DNA. The application of molecular diagnostics techniques, such as PCR, has led to the development of automated instruments that can identify a single infectious agent or multiple pathogens from a small amount of blood in less than 2 hr. The instruments can detect the presence of gram negative bacteria, gram positive bacteria, and yeast commonly associated with bloodstream infections. The instruments can also detect mutations in the genetic material of specific pathogens that code for antibiotic resistance.

This procedure is contraindicated for

    N/A

Indications

  • Determine sepsis in the newborn as a result of prolonged labor, early rupture of membranes, maternal infection, or neonatal aspiration
  • Evaluate chills and fever in patients with infected burns, urinary tract infections, rapidly progressing tissue infection, postoperative wound sepsis, and indwelling venous or arterial catheter
  • Evaluate intermittent or continuous temperature elevation of unknown origin
  • Evaluate persistent, intermittent fever associated with a heart murmur
  • Evaluate a sudden change in pulse and temperature with or without chills and diaphoresis
  • Evaluate suspected bacteremia after invasive procedures
  • Identify the cause of shock in the postoperative period

Potential diagnosis

Positive findings in:

  • Bacteremia or septicemia: Gram-negative organisms such as Aerobacter,Bacteroides,Brucella,Escherichia coli and other coliform bacilli, Haemophilus influenzae,Klebsiella,Pseudomonas aeruginosa, and Salmonella.
  • Bacteremia or septicemia: Gram-positive organisms such as Clostridium perfringens,Enterococci,Listeria monocytogenes,Staphylococcus aureus,S. epidermidis, and β-hemolytic streptococci.
  • Plague
  • Malaria (by special request, a stained capillary smear would be examined)
  • Typhoid fever

  • Note: Candida albicans is a yeast that can cause disease and can be isolated by blood culture.

Critical findings

  • Positive findings in any sterile body fluid such as blood

  • Note and immediately report to the health-care provider (HCP) positive results and related symptoms.

  • It is essential that a critical finding be communicated immediately to the requesting health-care provider (HCP). A listing of these findings varies among facilities.

  • Timely notification of a critical finding for lab or diagnostic studies is a role expectation of the professional nurse. Notification processes will vary among facilities. Upon receipt of the critical value the information should be read back to the caller to verify accuracy. Most policies require immediate notification of the primary HCP, Hospitalist, or on-call HCP. Reported information includes the patient’s name, unique identifiers, critical value, name of the person giving the report, and name of the person receiving the report. Documentation of notification should be made in the medical record with the name of the HCP notified, time and date of notification, and any orders received. Any delay in a timely report of a critical finding may require completion of a notification form with review by Risk Management.

  • Assess for signs and symptoms of sepsis or development of septic shock to include change in body temperature (greater than 101.3F/38.5C or less than 95F/35C; decreased systolic blood pressure (less than 90 mm Hg); increased heart rate (greater than 90 beats per minute); sudden change in mental status (restlessness, agitation or confusion); significantly decreased urine output (less than 30 mL/hour); increased respirations (greater than 20 breaths per minute); change in extremities (pale, mottled, and/or cyanotic in appearance); decreased or absent peripheral pulses). Note and immediately report to the health-care provider (HCP) positive results and related symptoms. Lists of specific organisms may vary among facilities; specific organisms are required to be reported to local, state, and national departments of health.

Interfering factors

  • Pretest antimicrobial therapy will delay or inhibit growth of pathogens.
  • Contamination of the specimen by the skin’s resident flora may invalidate interpretation of test results.
  • An inadequate amount of blood or number of blood specimens drawn for examination may invalidate interpretation of results.
  • Testing specimens more than 1 hr after collection may result in decreased growth or no growth of organisms. Delay in transport of specimen to the laboratory may result in specimen rejection. Verify submission requirements with the laboratory prior to specimen collection.
  • Collection of the specimen in an expired media tube will result in specimen rejection.
  • Negative findings do not ensure the absence of infection.

Nursing Implications and Procedure

Pretest

  • Positively identify the patient using at least two unique identifiers before providing care, treatment, or services.
  • Patient Teaching: Inform the patient this test can assist in identification of the organism causing infection.
  • Obtain a history of the patient’s complaints, including a list of known allergens, especially allergies or sensitivities to the materials in iodine solutions.
  • Obtain a history of the patient’s immune system, symptoms, and results of previously performed laboratory tests and diagnostic and surgical procedures.
  • Obtain a list of the patient’s current medications, including herbs, nutritional supplements, and nutraceuticals (see Effects of Natural Products on Laboratory Values online at DavisPlus).
  • Note any recent medications that can interfere with test results.
  • Review the procedure with the patient. Inform the patient that specimen collection takes approximately 5 min. Inform the patient that multiple specimens may be required at timed intervals. Address concerns about pain and explain to the patient that there may be some discomfort during the venipuncture. Consider the use of pediatric culture tubes, if appropriate for the patient’s age.
  • Sensitivity to social and cultural issues, as well as concern for modesty, is important in providing psychological support before, during, and after the procedure.
  • Note that there are no food or fluid restrictions unless by medical direction.

Intratest

  • Potential complications: N/A
  • Ensure that the patient has complied with medication restrictions prior to the procedure.
  • Avoid the use of iodine solutions if the patient has a history of severe allergic reaction to any of the materials in the iodine solution.
  • Instruct the patient to cooperate fully and to follow directions. Direct the patient to breathe normally and to avoid unnecessary movement.
  • Observe standard precautions, and follow the general guidelines in Patient Preparation and Specimen Collection. Positively identify the patient, and label the appropriate specimen containers with the corresponding patient demographics, date and time of collection, and any medication the patient is taking that may interfere with test results (e.g., antibiotics). Perform a venipuncture; collect the specimen in the appropriate blood culture collection container.
  • The high risk for contamination of blood cultures by skin and other flora can be dramatically reduced by careful preparation of the puncture site and collection containers before specimen collection. Cleanse the rubber stoppers of the collection containers with the appropriate disinfectant as recommended by the laboratory, allow to air-dry, and cleanse with 70% alcohol. Once the vein has been located by palpation, cleanse the site with 70% alcohol followed by swabbing with an iodine solution. The iodine solution should be swabbed in a circular, concentric motion, moving outward or away from the puncture site. The iodine solution should be allowed to completely dry before the sample is collected. If the patient is sensitive to iodine solutions, a double alcohol scrub or green soap may be substituted.
  • If collection is performed by directly drawing the sample into a culture tube, fill the aerobic culture tube first.
  • If collection is performed using a syringe, transfer the blood sample directly into each culture bottle.
  • Remove the needle, and apply direct pressure with a dry gauze to stop bleeding. Observe/assess venipuncture site for bleeding and secure gauze with adhesive bandage.
  • Promptly transport the specimen to the laboratory for processing and analysis.
  • More than three sets of cultures per day do not significantly add to the likelihood of pathogen capture. Capture rates are more likely affected by obtaining a sufficient volume of blood per culture.
  • The use of ARDs or resin bottles is costly and controversial with respect to their effectiveness versus standard culture techniques. They may be useful in selected cases, such as when septicemia or bacteremia is suspected after antimicrobial therapy has been initiated.
    • Disease SuspectedRecommended Collection
    Bacterial pneumonia, fever of unknown origin, meningitis, osteomyelitis, sepsisTwo sets of cultures, each collected from a separate site, 30 min apart
    Acute or subacute endocarditisThree sets of cultures, each collected from a separate site, 30–40 min apart. If cultures are negative after 24–48 hr, repeat collections
    Septicemia, fungal or mycobacterial infection in immunocompromised patientTwo sets of cultures, each collected from a separate site, 30–60 min apart (laboratory may use a lysis concentration technique to enhance recovery)
    Septicemia, bacteremia after therapy has been initiated, or request to monitor effectiveness of antimicrobial therapyTwo sets of cultures, each collected from a separate site, 30–60 min apart (consider use of ARD to enhance recovery)

Post-Test

  • Inform the patient that a report of the results will be made available to the requesting HCP, who will discuss the results with the patient.
  • Instruct the patient to resume usual medication as directed by the HCP.
  • Cleanse the iodine solution from the collection site.
  • Instruct the patient to report symptoms such as pain related to tissue inflammation or irritation.
  • Instruct the patient to report fever, chills, and other signs and symptoms of acute infection to the HCP.
  • Instruct the patient to begin antibiotic therapy, as prescribed. Instruct the patient in the importance of completing the entire course of antibiotic therapy even if no symptoms are present.
  • Inform the patient that preliminary results should be available in 24 to 72 hr, but final culture results are not available for 5 to 7 days. Test results for PCR methods are generally available a few hours after testing is completed.
  • Recognize anxiety related to test results. Discuss the implications of abnormal test results on the patient’s lifestyle. Provide teaching and information regarding the clinical implications of the test results, as appropriate.
  • Reinforce information given by the patient’s HCP regarding further testing, treatment, or referral to another HCP. Emphasize the importance of reporting continued signs and symptoms of the infection. Provide information regarding vaccine-preventable diseases where indicated (e.g., Haemophilus influenza, meningococcal disease). Provide contact information, if desired, for the Centers for Disease Control and Prevention (www.cdc.gov/vaccines/vpd-vac). Answer any questions or address any concerns voiced by the patient or family.
  • Depending on the results of this procedure, additional testing may be performed to evaluate or monitor progression of the disease process and determine the need for a change in therapy. Evaluate test results in relation to the patient’s symptoms and other tests performed.

Related Monographs

  • Related tests include bone scan, bronchoscopy, CBC, cultures (fungal, mycobacteria, throat, sputum, viral), CSF analysis, ESR, gallium scan, Gram stain, HIV-1/2 antibodies, MRI musculoskeletal, procalcitonin, PFT, radiography bone, and TB tests.
  • Refer to the Immune System table at the end of the book for related tests by body system.