Blood Collection Techniques (Venipuncture and Capillary/Dermal Puncture)
Core concepts
Venipuncture uses the median cubital vein first, then cephalic or basilic; inspect and palpate, and avoid areas with scars, hematoma, infection, or recent venipuncture. Apply the tourniquet 3 to 4 inches above the site for no more than one minute; release it as soon as blood flows. Use a 21- to 23-gauge needle for routine draws, bevel up, at a 15- to 30-degree angle. Anchor the vein below the puncture site and insert smoothly; do not probe. Follow the CLSI order of draw for additive tubes: blood culture, coagulation, serum, heparin, EDTA, and glycolytic inhibitor. For capillary puncture, choose the third or fourth finger, or the medial/lateral plantar heel in infants; warm the site, clean, and puncture across the ridges. Wipe away the first drop when policy requires, then fill and mix tubes promptly.
Question traps
Order-of-draw questions are common. Do not pump the fist vigorously, leave the tourniquet on during filling, or draw above an IV. Hemolysis traps include small needles, excessive vacuum, shaking, and pulling back a syringe plunger forcefully. In capillary collection, squeezing the site dilutes the sample with tissue fluid; the heel is not the central area, and fingersticks are not for infants.
Worked rule
If blood flow slows or stops, release the tourniquet and adjust the needle slightly; if flow does not return, withdraw, apply pressure, and perform a second attempt at a different site. Never probe blindly. One clean reattempt is safer than a prolonged, traumatic stick.