7.2 Vein Selection and Venipuncture Technique
Key Takeaways
- In the antecubital fossa, the median cubital vein is preferred, then the cephalic; the basilic is last because it lies near the brachial artery and median nerve.
- Tourniquet time is no more than about one minute; release the tourniquet before withdrawing the needle.
- Do not draw through a hematoma, above an IV, from an artery, or from a mastectomy-side arm without a documented exception.
- Palpate for a bouncy, non-pulsatile vein; visual-only selection and a pulse at the site are both failures.
- Use an evacuated-tube system for routine stable veins, a butterfly for small or difficult veins, and a syringe when vacuum would collapse the vein—never an arterial stick.
CMLA II.3.B.6–7 requires you to select the proper venipuncture site and perform venipuncture. The current standard on AMT CMLA-REF-2025-1 is CLSI PRE02, Collection of diagnostic venous blood specimens, 8th edition (2025), the successor to GP41. Chapter 6 named the devices; this section is how you choose a vein and use them without hitting an artery, a nerve, a hematoma, or a running IV.
Quick Answer: Median cubital first, then cephalic, basilic last (artery and median nerve). Palpate; pulse means artery. Tourniquet ≤1 minute. Bevel up at about 15–30 degrees, anchor below the site, release the tourniquet before the needle comes out. Never draw through a hematoma, above an IV, or from an artery.
Antecubital veins: preferred, second, last
The antecubital fossa is the first-choice region in adults. Three superficial veins matter on CMLA.
The median cubital vein is preferred. It is usually well anchored in the center of the fossa, least likely to roll, and in typical H-shaped and M-shaped patterns it sits farther from the brachial artery and median nerve than the basilic vein.
The cephalic vein is lateral (thumb side) and is the second choice when the median cubital is scarred, sclerosed, or absent. It can lie deeper in patients with more subcutaneous tissue, so palpation matters more than a faint blue shadow.
The basilic vein is medial (pinky side) and is last. It tracks close to the brachial artery and median nerve. A miss here is the classic arterial puncture or nerve injury. Last does not mean never; it means after safer veins are unavailable.
| Vein | Location in the fossa | Why chosen or avoided |
|---|---|---|
| Median cubital | Center | Preferred: stable, lower artery and nerve risk |
| Cephalic | Lateral (thumb side) | Second: acceptable; may roll or sit deep |
| Basilic | Medial (pinky side) | Last: brachial artery and median nerve nearby |
Dorsal hand veins are a fallback after antecubital sites fail, usually with a butterfly. Ankle or foot veins need provider approval because of thrombosis risk. Do not use the palmar wrist, where the radial artery and nerves are shallow. Full capillary technique, including infants, is Chapter 8—not a substitute for a careless basilic stick.
Palpation versus visual only
Palpate with a clean gloved fingertip. A suitable vein is bouncy and resilient. A rigid cord is often sclerotic. A beat is not a strong vein.
Visual-only selection is a CMLA trap. Arteries can look blue under thin skin. Thrombosed veins can look full. Deep usable veins may not show. If you feel a pulse at the proposed site, you are on or next to an artery. Routine CMLA collections are venous, never arterial. Arterial puncture for blood gases is a specialized procedure outside ordinary assistant venipuncture.
If bright-red blood pulses into the tube, a hematoma expands rapidly, or pain shoots in a nerve distribution, remove the needle, apply firm prolonged pressure per policy, and do not relabel the event as a normal venous draw.
Sites you do not use
Do not draw through a hematoma. Tissue fluid and lysed cells contaminate the specimen and hemolyze it (Section 7.4).
Do not draw above (proximal to) an IV. Infusate dilutes and contaminates chemistry and coagulation results. Prefer the other arm. If that arm is unusable, follow PRE02 and SOP: stop the infusion when required, wait the specified interval, draw below (distal to) the IV, and discard the specified volume.
Do not use the mastectomy-side arm without a documented exception, and do not apply a tourniquet to an AV fistula or graft arm (Section 7.1). Skip infected, burned, heavily scarred, or edematous skin when another site exists. A PICC or other vascular-access arm is restricted unless SOP names a workaround.
Never draw from an artery because it looks like an easy vein.
Tourniquet, angle, anchor, release
Apply the tourniquet about 3–4 inches above the site, tight enough to distend veins but not to erase the distal pulse. Limit time to about one minute. Prolonged occlusion hemoconcentrates proteins, cells, and potassium (Section 7.1). If you must search again, release, wait about two minutes, and reapply.
Cleanse per SOP (typically 70% isopropyl alcohol) and allow to dry. Wet alcohol stings and hemolyzes (Section 7.4).
Anchor the vein by pulling the skin taut below the site with the thumb. Do not use a two-finger C-hold that parks a finger in the needle's path after the stick.
Insert bevel up at a shallow angle, typically 15–30 degrees for a straight evacuated-tube needle (often shallower with a butterfly). A 90-degree jab is not venipuncture.
Once blood flows, release the tourniquet before withdrawing the needle—and within the one-minute window, ideally as soon as flow is established. Leaving it on until after withdrawal raises hematoma risk and prolongs hemoconcentration. Then withdraw the needle and apply pressure. Full post-puncture care, labeling, and transport are Chapter 8.
Evacuated tube, butterfly, and syringe
An evacuated-tube system (straight safety needle plus adapter) is the default for a stable adult antecubital vein.
A butterfly (winged infusion set) is for small, fragile, rolling, or hand veins and for awkward angles. Extra tubing can underfill a citrate tube because air in the line occupies volume. When a light-blue top is the first tube on a butterfly, many procedures require a discard tube so the 9:1 fill is real (Section 7.3).
A syringe is for veins that would collapse under evacuated-tube vacuum. Move syringe blood into tubes with a transfer device (Chapter 6). Do not force the plunger. Do not puncture a stopper with an exposed needle.
Device choice follows the vein. Neither a butterfly nor a syringe authorizes an arterial collection.
In practice
You palpate a bouncy median cubital without a pulse, apply a tourniquet, cleanse, let alcohol dry, anchor below, enter bevel up at a shallow angle, and release the tourniquet as soon as tubes are filling—well under one minute—then withdraw. You skip a spectacular basilic vein next to a pulse, skip a green hematoma, and skip the arm with the running IV. If the only remaining vein is a small dorsal hand vein, you switch to a butterfly; if that vein flutters and collapses under vacuum, you switch to a syringe plus transfer device.
Exam traps
- Basilic first because it looks big is the nerve-and-artery trap.
- Visual-only selection without palpation.
- Tourniquet left on until after the needle is out.
- Drawing through a hematoma or above an IV.
- Calling a pulse a strong vein.
- Using a butterfly for every healthy adult antecubital draw.
- Treating syringe technique as permission to skip order of draw or a transfer device.
When a stem names a site, answer with artery, nerve, hematoma, IV, and restricted-arm rules—not with whichever blue line is most obvious.
In the antecubital fossa, which vein-selection sequence is correct and why?
Which venipuncture technique statement matches CLSI PRE02 practice?
Which collection-site decision follows accepted venous-collection practice?