Equipment Selection and Maintenance
Match equipment to the task. Needle gauge and length depend on vein size and draw volume: larger gauges (21–23 G) for routine adult venipuncture, smaller gauges (23–25 G) for fragile or pediatric veins (which increase hemolysis risk). Use a butterfly (winged set) for small or fragile veins, and a syringe for draws where vacuum could collapse a vein or when volume control matters. Know the order of draw for multiple tubes and the additives in each; know that tubes must be at the correct fill volume for additive-to-blood ratio, especially citrate tubes.
Traps: using an expired tube or a tube with a cracked rim; over- or under-filling citrate tubes (affects coagulation results); drawing from an arm with a hematoma; and forgetting to mix tubes immediately by inversion the correct number of times. Another trap is selecting a lancet depth inappropriate for an infant heel. Also know that tourniquet time over one minute can raise potassium and other analytes.
Maintenance: inspect supplies, rotate stock, check expiration dates, and never use damaged devices. Safety-engineered devices must be activated immediately after use.
Worked rule of thumb: if a tube fills short, discard and recollect rather than topping off from another tube. For coagulation studies, the tube must be filled to the indicated line and mixed gently; a short draw invalidates the result.