Venipuncture: drawing blood samples
- Procedure
Identify the patient properly, choose a suitable vein, disinfect and let it dry, and fill the tubes in the correct order.
What it is
Venipuncture draws venous blood for the laboratory, almost always from the antecubital fossa. The 2010 WHO guidelines on drawing blood set the procedure out in steps: assemble equipment, identify and prepare the patient, select the site, hand hygiene and gloves, disinfect, puncture, fill the tubes in the correct order, discard the sharp, label and prepare for transport. The most common errors are not technical but in identification and labelling. The median cubital vein is usually the easiest and safest.
Indications
- Ordered laboratory tests that need venous blood.
- Scheduled serial samples (for example, fasting tests).
- Blood cultures and other special tests, with their own requirements.
Contraindications and precautions
- Do not draw from an arm with an infusion or a peripheral line in use: fluid and drugs alter the result.
- Avoid the arm on the side of a mastectomy and, per protocol, an arm with a dialysis fistula.
- Do not puncture where veins branch or over the basilic vein, which has an artery and a nerve nearby.
- Ask about allergies, fear of needles or previous fainting; if at risk, have the patient lying down.
- Explain the test and obtain verbal consent: the patient may refuse at any time before the puncture.
Equipment
- Laboratory tubes per the request and an evacuated-tube system with holder, or syringe and needle, or a winged needle.
- A clean tourniquet, non-sterile gloves and 70 % alcohol swabs.
- Dry gauze or cotton wool and a plaster or tape.
- A sharps container within arm's reach.
- Labels, the laboratory request and a transport bag.
Step by step (and why)
- Assemble the equipment and check the request — having everything ready avoids leaving the tourniquet on.
- Identify the patient by asking their name and compare it with the request; explain and get consent — it avoids wrong-patient samples.
- Choose a visible, straight vein in the antecubital fossa and apply the tourniquet 4 to 5 fingers above — it fills the vein without harm.
- Hand hygiene and gloves — it protects the patient and the staff.
- Disinfect with 70 % alcohol for 30 seconds and let it dry; do not touch the site again — wet alcohol haemolyses and does not disinfect.
- Anchor the vein with the thumb below and puncture at 30° or less — a low angle lowers the risk of going through the vein.
- Fill the tubes in the recommended order and invert them as the lab specifies — it avoids cross-contamination of additives.
- Release the tourniquet, withdraw the needle and press with gauze, arm straight — bending the arm favours a haematoma.
- Discard the needle into the sharps container without recapping and label the tubes in front of the patient — it avoids needlesticks and label errors.
- Check the site, pack the samples in a sealed bag and record — a well-transported sample arrives usable.
Complications
- Haematoma and bruising from a failed puncture or from bending the arm.
- Fainting (vasovagal response), especially in anxious people or those with a history.
- Nerve injury or accidental arterial puncture.
- Haemolysis of the sample from wet alcohol, a needle that is too small or forcing blood with the syringe.
- Needlestick injury to staff from recapping or poor disposal.
Next step: when to call for help
- Limit attempts per protocol; in children, the WHO asks for no more than two without a second opinion. Ask a more experienced colleague for help.
- If the patient feels faint or faints, stop, remove the needle, lay them down and report.
- Report electric, radiating pain (possible nerve injury) or a growing haematoma.
- If you have a needlestick, wash the area and follow the institution's exposure pathway at once.
Test yourself
Think of the answer, then tap the question to see it.
Where is the tourniquet placed for venipuncture?
About 4 to 5 finger widths above the puncture site, and it is released before the needle is withdrawn, never left on for 2 minutes or more.
Why must the alcohol dry before puncturing?
Because alcohol needs contact time to disinfect and, if still wet, it can haemolyse the sample.
Why is blood not taken from the arm with an infusion running?
Because the fluid and medicines in the infusion dilute or alter the sample and give false results.
What is done with the needle at the end of venipuncture?
It is discarded at once, without recapping, together with the device into a sharps container within arm's reach.
Connections
Educational content for students; it does not replace your institution's protocols, supervised clinical training or a prescriber's order. Dose-calculation examples use made-up numbers: they are educational, not a clinical order.
Sources: WHO guidelines on drawing blood: best practices in phlebotomy (World Health Organization, 2010); Blood Culture Contamination: An Overview for Infection Control and Antibiotic Stewardship Programs Working with the Clinical Laboratory (Centers for Disease Control and Prevention (CDC), 2024).
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Representative model, for educational purposes only.