Phlebotomy

Phlebotomy is a technique in which a needle is temporarily inserted into a vein to provide venous access for venous blood sampling. ^{[1, 2, 3]}  Veins have a three-layered wall composed of an internal endothelium surrounded by a thin layer of muscle fibers, which in turn is surrounded by a layer of connective tissue.

Identification of the optimal site for venous access (see Technical Considerations) involves both visual and tactile evaluation. After applying a venous tourniquet, the physician should inspect and palpate potential sites, starting with the nondominant extremity. On palpation, the vein should be soft and bouncy, it should refill after being depressed, and it ideally should be well supported by the surrounding tissue.

Phlebotomy is commonly performed with either an evacuated tube system (eg, Vacutainer; BD, Franklin Lakes, NJ) or a syringe and needle or winged butterfly needle device (see Technique).

Indications for phlebotomy include the following:

• Blood sampling
• Short-term infusion (via butterfly needle)

Contraindications for phlebotomy include the following:

• Evidence of cellulitis or abscess
• Venous fibrosis on palpation
• Presence of a hematoma
• Presence of a vascular shunt or graft
• Presence of a vascular access device

Anatomy

The superficial veins of the upper extremities, particularly those in the antecubital fossa, are the ones most commonly selected for phlebotomy because they are usually readily visible and easily palpable. The antecubital fossa contains four veins (see the images below). Of these, the median cubital vein is usually the vein of choice for phlebotomy: It is typically more stable (less likely to roll), it lies more superficially, and the skin overlying it is less sensitive than the skin overlying the other veins.

In many cases, the metacarpal veins are easily visualized and palpated (see the image below). However, obtaining needle access on the dorsal hand is more painful, and the metacarpal veins are more likely to roll and collapse on vacuum application than the antecubital veins are.

It appears that the device used to collect blood is the strongest independent predictor of hemolysis in blood samples drawn in the emergency department (ED). An ED study suggested that the most effective strategy to reduce the rate of hemolysis in the ED is to use butterfly needles for phlebotomy rather than intravenous catheters. ^[4]