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Microbiology

Blood Culture

Blood culture collection is a critical procedure in diagnosing bloodstream infections. It requires meticulous attention to detail to prevent contamination and ensure accurate results

Importance

  • Diagnosing Bacteremia/Fungemia: Blood cultures are the gold standard for detecting bacteria or fungi in the bloodstream, which can cause severe infections like sepsis
  • Guiding Treatment: Identifying the causative organism and its antibiotic sensitivities is crucial for selecting the appropriate antimicrobial therapy
  • Monitoring Infection Control: Blood culture results help track and manage healthcare-associated infections (HAIs), contributing to infection control efforts
  • Preventing False Positives: Contamination during collection can lead to false-positive results, resulting in unnecessary antibiotic use, prolonged hospital stays, and increased healthcare costs

Key Principles

  • Sterile Technique: Strict adherence to sterile technique is paramount to minimize the risk of contamination
  • Skin Antisepsis: Thorough disinfection of the venipuncture site is crucial to eliminate skin flora that can contaminate the blood sample
  • Blood Volume: Collecting the appropriate volume of blood is essential for optimal recovery of microorganisms
  • Collection Timing: Ideally, blood cultures should be collected before starting antibiotic therapy and when the patient is experiencing signs and symptoms of infection
  • Number of Sets: Collecting multiple blood culture sets (usually two or three) increases the sensitivity of detection

Materials and Equipment

  • Blood Culture Bottles
    • Aerobic Bottle: For the growth of aerobic bacteria
    • Anaerobic Bottle: For the growth of anaerobic bacteria
    • Pediatric Bottle: For smaller blood volumes from pediatric patients
  • Antiseptic Solutions
    • Chlorhexidine Gluconate: A commonly used antiseptic with broad-spectrum activity
    • Iodine/Iodophor: Another effective antiseptic
    • Alcohol (70% Isopropyl): Used for initial skin cleaning
  • Sterile Gloves: To protect the healthcare worker and maintain sterility
  • Tourniquet: To distend the veins for easier venipuncture
  • Sterile Needles and Syringes or Blood Collection Sets
    • Needles: Typically 21-23 gauge
    • Syringes: Appropriate size for the required blood volume
    • Blood Collection Sets (Butterfly Needles): Often used for patients with difficult veins
  • Sterile Gauze Pads: For cleaning and applying pressure after venipuncture
  • Bandage: To cover the venipuncture site
  • Sharps Container: For safe disposal of used needles and syringes
  • Blood Culture Collection Tray: To organize supplies

Procedure

  1. Preparation
    • Review the physician’s order and verify the patient’s identity using two identifiers
    • Explain the procedure to the patient
    • Gather all necessary supplies and equipment
    • Perform hand hygiene
    • Don sterile gloves
  2. Site Selection
    • Choose a venipuncture site that is free from lesions, scars, or hematomas
    • Avoid drawing blood from an IV line unless specifically ordered by the physician
  3. Skin Antisepsis
    • Apply the tourniquet
    • Clean the venipuncture site with 70% isopropyl alcohol, using a circular motion, starting from the center and moving outward. Allow to air dry completely (at least 30 seconds)
    • Apply chlorhexidine gluconate or iodine/iodophor using a similar circular motion. Allow to air dry completely (at least 30 seconds)
      • Important: Do not touch the disinfected site after cleaning. If you need to palpate the vein again, you must repeat the disinfection process
  4. Blood Collection
    • Perform venipuncture using sterile technique
    • Collect the appropriate volume of blood into the syringe or blood collection set
      • Adults: Typically 8-10 mL per bottle (aerobic and anaerobic). Follow bottle manufacturer’s instructions
      • Pediatrics: Volume depends on the age and weight of the child. Follow bottle manufacturer’s instructions
    • Release the tourniquet
    • Apply pressure to the venipuncture site with sterile gauze
    • Engage safety device and dispose of the needle and syringe or blood collection set in the sharps container
  5. Inoculation of Blood Culture Bottles
    • Clean the tops of the blood culture bottles with alcohol swabs
    • Inoculate the blood culture bottles in the correct order (anaerobic first, if using a butterfly needle)
    • Mix the blood with the culture media by gently inverting the bottles several times
    • Important: Do not overfill or underfill the blood culture bottles. Follow the manufacturer’s instructions for the correct blood-to-broth ratio
  6. Post-Collection
    • Apply a bandage to the venipuncture site
    • Label the blood culture bottles with the patient’s information, date, time, and initials of the person collecting the sample
    • Transport the blood culture bottles to the laboratory promptly

Specific Considerations

  • Collection from IV Lines
    • Blood cultures should ideally be collected by venipuncture, not from IV lines, due to the increased risk of contamination
    • If blood cultures must be collected from an IV line, follow a strict protocol, including:
      • Disinfecting the IV port thoroughly with alcohol and chlorhexidine
      • Discarding the initial aliquot of blood
  • Patients on Antibiotics
    • If possible, collect blood cultures before starting antibiotic therapy
    • If the patient is already on antibiotics, note this on the requisition form. The lab may use special media to neutralize the antibiotics
  • Pediatric Blood Cultures
    • Use pediatric blood culture bottles designed for smaller blood volumes
    • Follow specific guidelines for blood volume based on the child’s age and weight

Common Errors and How to Avoid Them

  • Inadequate Skin Antisepsis
    • Solution: Emphasize the importance of proper skin preparation techniques, including the use of appropriate antiseptics and sufficient drying time
  • Contamination
    • Solution: Reinforce sterile technique principles, including hand hygiene, sterile gloves, and avoiding touching the venipuncture site after disinfection
  • Insufficient Blood Volume
    • Solution: Provide clear guidelines on the correct blood volume for each type of blood culture bottle and patient population
  • Improper Inoculation Technique
    • Solution: Train personnel on the correct order of inoculation, mixing techniques, and avoiding overfilling or underfilling the bottles

Documentation and Quality Control

  • Documentation
    • Record the date and time of collection, the site of venipuncture, the volume of blood collected, the lot numbers of the blood culture bottles, and any deviations from standard procedure
  • Quality Control
    • Monitor contamination rates and investigate any trends or patterns
    • Provide ongoing training and education to personnel on blood culture collection techniques
    • Periodically review and update blood culture collection protocols to ensure they are consistent with current best practices
    • Participate in proficiency testing programs to assess the accuracy of blood culture collection procedures

Key Terms

  • Bacteremia: The presence of bacteria in the bloodstream
  • Fungemia: The presence of fungi in the bloodstream
  • Sepsis: A life-threatening condition caused by the body’s response to an infection
  • Sterile Technique: A set of practices and procedures designed to minimize the risk of contamination
  • Skin Antisepsis: The process of disinfecting the skin to reduce the number of microorganisms
  • Blood Culture Set: A pair of blood culture bottles (aerobic and anaerobic) collected from a single venipuncture
  • Venipuncture: The process of puncturing a vein to collect blood