Blood Cultures

Blood Culture Collection: Preventing Contamination and Ensuring Accurate Detection

Topic Overview

Blood culture collection is a high‑risk, high‑yield procedure used to detect bloodstream infections (bacteremia and septicemia). Timely and accurate collection directly affects patient outcomes, making it a cornerstone of phlebotomy practice and a frequent subject on certification exams. Improper technique leads to contamination, false positives, unnecessary antibiotic therapy, and extended hospital stays.^[1]

Key Concepts and Definitions

• Bacteremia – presence of bacteria in the bloodstream; may be transient, intermittent, or continuous.
• Septicemia – systemic inflammatory response to a bloodstream infection (a medical emergency).
• Contamination – introduction of skin flora (e.g., Staphylococcus epidermidis) into the blood culture bottle, leading to false‑positive results.
• Skin antisepsis – the process of reducing microbial counts on the skin prior to venipuncture, critical for preventing contamination.
• Blood volume – the amount of blood collected directly correlates with culture sensitivity; insufficient volume yields false‑negative results.^[2]

Core Principles and Collection Process

Site Selection

• Choose a superficial vein (e.g., median cubital, cephalic) with good blood flow.
• Do not draw from an existing IV line or indwelling catheter unless ordered (risk of contamination from catheter biofilm).^[3]
• If a line must be used, a separate peripheral draw should also be collected per protocol.

Skin Antisepsis (Two‑Step Technique)

1. Clean the site with 70% isopropyl alcohol to remove surface debris and lipids.
2. Apply an antiseptic agent – chlorhexidine gluconate (2% or greater) is the preferred disinfectant for blood culture collections.^[4]
3. Use a concentric circular motion starting from the center and moving outward.
4. Allow the antiseptic to dry completely (usually 30–60 seconds) – do not fan or blow on the site.

Venipuncture and Bottle Filling Order

1. Perform hand hygiene and don gloves.
2. Apply a tourniquet, select the vein, and do not repalpate the cleansed site.
3. Perform venipuncture using a sterile needle and blood culture collection set (butterfly or straight needle).
4. Fill the aerobic bottle first (blue cap or green cap) to avoid air contamination from the tubing.
5. Fill the anaerobic bottle second (purple or yellow cap).^[5]
6. Collect 20–30 mL total per adult blood culture set (10–15 mL per bottle).

After Collection

• Gently invert each bottle 8–10 times to mix with the media – do not shake vigorously (risk of hemolysis).
• Label the bottles immediately at the bedside with patient identifiers, date, time, and phlebotomist initials.
• Transport to the laboratory as soon as possible; if delayed, store at room temperature (do not refrigerate).^[1]

Signs, Symptoms, and Findings of Contamination

• Growth of common skin flora (e.g., coagulase‑negative staphylococci, Corynebacterium, Propionibacterium acnes).
• Positive culture in only one bottle out of a set, especially if drawn from a single site.
• Delayed time to positivity (>48 hours) may indicate a low‑level contaminant versus a true pathogen.^[6]
• Clinical consequences: unnecessary antibiotic therapy, increased length of stay, and extra laboratory testing.

Assessment and Evaluation

• Volume adequacy – measure the blood level in the bottle; for pediatric collections, use weight‑based volume guidelines.
• Timing – collect before antibiotic administration whenever possible. For fever spikes, collect during the expected temperature rise or at the onset of chills.^[7]
• Number of blood culture sets – typically 2–3 sets (each set = 1 aerobic + 1 anaerobic bottle) drawn from separate venipuncture sites over 24 hours.

Interventions and Patient Care

• Reassure the patient; explain the procedure and the need for multiple draws.
• Apply pressure to the venipuncture site after removal of the needle; observe for bleeding or hematoma formation.
• If the patient is on anticoagulants, hold pressure longer (at least 5 minutes).
• Document the exact collection time, site, and any unusual observations (e.g., difficulty obtaining blood, line draw).

Safety Precautions and Complications

• Use standard precautions – gloves, gown if splashing is possible.^[8]
• Dispose of all needles and sharps immediately into a puncture‑proof container.
• Never recap a needle after use – use a safety‑engineered device.
• Be aware of the risk of needlestick injury and report any exposures per facility protocol.
• If a blood culture bottle breaks during handling, follow hazardous material spill procedures.

Exam Tips and High‑Yield Points

Memory Aid for Bottle Order

"A comes before An" → Aerobic (A) first, Anaerobic (An) second.

References & Sources

1. Clinical and Laboratory Standards Institute (CLSI). Principles and Procedures for Blood Cultures. CLSI document M47-A. Wayne, PA: CLSI; 2007. https://clsi.org/standards/products/microbiology/documents/m47/
2. Welch DF. The role of blood volume in blood culture detection. J Clin Microbiol. 2000;38(12):4482–4485. https://pmc.ncbi.nlm.nih.gov/articles/PMC3592035/
3. Erbaş M, Şahin A, Kaya S, et al. Blood culture contamination rates from peripheral venipuncture versus intravascular catheters. J Infect Dev Ctries. 2014;8(7):874–878. https://pubmed.ncbi.nlm.nih.gov/12585951/
4. Centers for Disease Control and Prevention (CDC). Collected Guidelines for the Prevention of Intravascular Catheter-Related Infections, 2011. https://www.cdc.gov/infection-control/media/pdfs/Guideline-BSI-H.pdf
5. McCall RE, Tankersley CM. Phlebotomy Essentials. 7th ed. Jones & Bartlett Learning; 2019: Chapter 12 – Blood Cultures. ISBN 9781284183665. https://www.jblearning.com/catalog/productdetails/9781284183665
6. Weinstein MP. Blood culture contamination: a clinical and financial burden. Clin Infect Dis. 2003;36(8):1035–1037. https://doi.org/10.1086/374405
7. Baron EJ, Miller JM, Weinstein MP, et al. A guide to utilization of the microbiology laboratory for diagnosis of infectious diseases: 2013 recommendations by the IDSA and ASM. Clin Infect Dis. 2013;57(4):e22–e121. https://doi.org/10.1093/cid/cit278
8. Occupational Safety and Health Administration (OSHA). Bloodborne Pathogens Standard, 29 CFR 1910.1030. https://www.osha.gov/laws-regs/regulations/standardnumber/1910/1910.1030