Venipuncture
The puncture of a vein with a needle to collect blood specimens or establish intravenous access.
The exam rarely asks “what is venipuncture” — it tests the order of draw and the site you must NOT use. The CLSI sequence is blood cultures → light-blue citrate → red → gold/SST → green → lavender (EDTA) → gray, and the classic trap is drawing the lavender tube too early: EDTA carryover falsely lowers calcium and elevates potassium. The other reliable “tell” is a forbidden arm: avoid the side of a mastectomy, AV fistula/graft, or active IV infusion. When you must use an arm with a running line, draw distal (below) the IV, never above it, since fluid above the site dilutes the sample. When values look bizarre, suspect hemolysis from too-narrow a needle, excessive tourniquet time (keep it under 1 minute), or vigorously shaking the tubes — a frequent cause of spurious hyperkalemia.
Don’t confuse the related concepts: venipuncture is the technique of accessing the vein, the specimen is the sample obtained, and the laboratory is where it is analyzed — questions blur these to make you misjudge what went wrong. A catheter drains or delivers fluids, whereas venipuncture is for collection or short-term IV access.
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