Venipuncture & Capillary Puncture Technique

Venipuncture Procedure — Step by Step

1. Verify the requisition and greet the patient; explain the procedure in plain language.
2. Identify the patient using two identifiers (name and date of birth) and confirm the requisition matches.
3. Verify fasting or diet restrictions if required for the ordered test.
4. Position the patient's arm, extended and supported, angled slightly downward.
5. Apply the tourniquet 3-4 inches above the intended site; it must be released within one minute of application to prevent hemoconcentration, which falsely elevates protein-bound analytes.
6. Palpate and select a vein; ask the patient to make a single fist without repeatedly pumping it, since repeated pumping can also cause hemoconcentration and falsely elevate potassium.
7. Cleanse the site with 70% isopropyl alcohol in a circular motion from the center outward, then allow it to air dry — do not blow on or fan it, and do not re-touch the site.
8. Anchor the vein by pulling the skin taut one to two inches below the site with the thumb.
9. Insert the needle, bevel up, at a 15-30 degree angle to the skin — this shallow angle avoids passing through the vein into deeper tissue and reduces the risk of nerve or artery involvement.
10. Fill tubes in CLSI order of draw, releasing the tourniquet as soon as blood flows, and always within one minute.
11. Remove the needle, activate the safety shield, and apply pressure with gauze; do not have the patient bend the elbow, which increases hematoma risk.
12. Label all tubes at the bedside, in front of the patient, before leaving the room.

Collection Method Comparison

• ETS (evacuated tube system) — the default method for adults with accessible, normal-caliber veins; allows multiple tubes to be filled from a single puncture.
• Winged infusion (butterfly) set — preferred for small, fragile, or hand veins, for pediatric and geriatric patients, and for short or angled sticks; the flexible tubing allows a lower insertion angle.
• Syringe method — used for veins that are fragile or likely to collapse under ETS vacuum pressure; blood is drawn by hand and transferred into tubes through a safety transfer device, never by removing the needle and injecting directly, which risks hemolysis and needlestick injury.

Capillary (Dermal) Puncture Technique

Capillary puncture is used when veins are inaccessible, for small blood volumes, for infants and young children, or for point-of-care testing.

Finger puncture (older children and adults):

• Site: the palmar surface of the distal, lateral third or fourth (ring) fingertip, slightly off-center from the pad — the very center and tip have more nerve endings and less tissue depth.
• Avoid the thumb, index finger (more nerve endings and calluses), and pinky (too little tissue).
• Clean with alcohol and let dry, then puncture perpendicular to the fingerprint ridges with a safety lancet.
• Wipe away the first drop of blood with clean gauze — it is diluted with tissue (interstitial) fluid and alcohol residue, which would skew results.
• Do not milk or squeeze the puncture site aggressively; excessive squeezing hemolyzes cells and introduces tissue fluid into the sample.

Heel puncture (infants under approximately one year):

• Site: the medial or lateral plantar surface of the heel — never the posterior curvature, due to the risk of striking the calcaneus bone, and never an area of prior puncture.
• Puncture depth is limited, generally under 2.0 mm, because an infant's heel bone lies close to the skin surface; too deep a puncture risks osteomyelitis (bone infection or injury).
• Warming the heel for a few minutes beforehand can increase blood flow and ease collection.

Attempt Limits and Escalation

Most facilities limit a single phlebotomist to two venipuncture attempts on a patient. If blood cannot be obtained after two tries, the phlebotomist should stop, explain the situation to the patient, and request assistance from another phlebotomist, a nurse, or a provider rather than continuing to attempt punctures. Repeated unsuccessful attempts increase patient pain, hematoma risk, and anxiety, and can also signal that a different collection method, such as a smaller-gauge butterfly or an alternate site, is needed.

Capillary Collection Devices

Capillary blood is collected into narrow microhematocrit or microtainer tubes. A warming device, heated to about 41-42 degrees Celsius, is sometimes applied to the puncture site beforehand to increase blood flow by arterializing the capillary bed — a technique especially useful for blood gas or CBC collection in infants.

Special-Situation Sites

Following these technique standards — correct angle, tourniquet timing, vein anchoring, and site-specific cautions — is what separates a safe, single-attempt draw from one that causes a hematoma, nerve injury, or an inaccurate result.