Materiales de Estudio

Phlebotomy is memorization-heavy and unforgiving: the order of draw, the tube additives, the angle, and the specimen handling are either right or wrong, and a small error invalidates a result. Build a mental table for the tubes and drill it until recall is instant. Two rules frame the whole chapter: follow the order of draw to prevent additive carryover, and label every tube at the bedside before you leave the room. (Reminder: whether a patient care technician draws blood at all is set by your state, certification, and employer — see the disclaimer.)

4.1 Order of Draw and Tube Additives

The order of draw exists to prevent additive from one tube contaminating the next, which would skew results. The standard venous order (CLSI GP41) is:

1. Blood culture bottles / sterile tubes — first, always, to maintain sterility and prevent contamination.
2. Light blue — sodium citrate (coagulation, e.g., PT/INR); drawn immediately after cultures.
3. Red or gold/SST — serum. A plain red tube has no additive and yields serum after the blood clots; an SST (gold/tiger) adds a clot activator and gel separator.
4. Green — heparin (plasma chemistry).
5. Lavender (purple) — EDTA (hematology, e.g., CBC).
6. Gray — sodium fluoride (preserves glucose and lactate).

Memorize what each additive is for: lavender/EDTA = CBC and hematology; green/heparin = plasma chemistry; gray/sodium fluoride = glucose/lactate; light blue/citrate = coagulation.

4.2 Venipuncture Technique

Angle. Insert the needle at a 15 to 30 degree angle, bevel up. Too steep (90°) passes through the vein; too shallow (parallel) never enters it.

Vein selection. The median cubital vein in the antecubital area is the first choice — large, well-anchored, and away from the artery and major nerves. The cephalic is a second choice; the basilic is used with caution because it lies near the brachial artery and nerves.

Tourniquet time. Leave the tourniquet on no longer than 1 minute to prevent hemoconcentration, which falsely elevates results such as potassium and protein. Release it once blood flow is established.

Identify the patient with two identifiers before collecting any specimen — full name and date of birth are typical. A room or bed location is never an identifier.

Choose the arm and site with care. Avoid drawing from an arm on the side of a mastectomy with lymph-node removal, an arm with an active IV above the intended site (which dilutes the sample), and any area of hematoma, scarring, edema, or a fistula/graft. When only an IV arm is available, the draw is done below the IV after it has been paused per protocol, or the other arm or a different site is used — decisions that belong to the nurse when in doubt.

Fill coagulation tubes completely. A light-blue citrate tube must be filled to the line to keep the 9-parts-blood-to-1-part-additive ratio; a short-draw blue tube is rejected because it falsely prolongs clotting times.

Manage a fainting patient. If a patient becomes pale, sweaty, and light-headed (presyncope) during a draw, stop immediately, remove the needle and apply pressure, and lower the patient's head or lay them flat while you stay with them. You never continue the draw "to finish quickly" or walk a woozy patient to a chair.

4.3 Capillary Collection

Infant heel sticks are performed on the medial or lateral (side) plantar surface of the heel, avoiding the center of the heel and the bone (calcaneus) beneath it.

The capillary order of draw differs from venous: collect blood gases first, then EDTA (hematology), then other additive tubes, then serum. EDTA is collected early in a capillary draw to get a well-mixed hematology sample before clotting begins. Wipe away the first drop when indicated, as it may be diluted with tissue fluid.

4.4 Specimen Handling and Quality

Mix, do not shake. Gently invert additive tubes the recommended number of times immediately after collection to mix the additive. Shaking causes hemolysis — ruptured red cells that falsely elevate results such as potassium — as do too-small needles and excessive tourniquet time.

Label at the bedside. Label every tube immediately after collection, in the patient's presence, with the patient's name, identifiers, date, time, and your initials. Labeling later at the desk, or pre-labeling before the patient arrives, invites a wrong-patient error.

Confirm fasting status. For fasting tests (typically 8–12 hours), confirm and document whether the patient actually fasted; if a patient scheduled for a fasting glucose reports eating, notify the nurse or provider and document the non-fasting status before proceeding.

Key Numbers & Facts — Chapter 4 (memorize cold)

Clinical Walkthrough — A Multi-Tube Draw

Orders come in for a coagulation panel, a chemistry panel, and a CBC. You confirm the patient with two identifiers, apply the tourniquet, and select the median cubital vein. You cannot find it for almost two minutes of palpating — stop: the tourniquet has been on too long (over one minute), so you release it, rest the arm, and reapply just before puncture, or the potassium will read falsely high. You enter at about 20°, bevel up, and draw in order: light blue citrate for the coagulation panel, then red/gold for chemistry, then lavender EDTA for the CBC. You gently invert each additive tube — no shaking, which would hemolyze the CBC and raise the potassium — and label every tube at the bedside before leaving. Every decision traces back to a number in the cram box.

Exam Traps — Chapter 4

• The order-of-draw carryover trap. Cultures first; light blue before lavender and gray. EDTA carried into a chemistry tube skews potassium and calcium.
• The tube-to-test mismatch trap. CBC = lavender/EDTA; glucose = gray/sodium fluoride; coagulation = light blue/citrate. Test-writers pair the right tube with the wrong test.
• The angle trap. Venipuncture is 15–30°, bevel up — not 90°, not parallel.
• The shake trap. Additive tubes are gently inverted; shaking causes hemolysis and a redraw.
• The label-later trap. Label at the bedside immediately, never at the desk afterward and never before the patient arrives.
• The tourniquet trap. Over 1 minute causes hemoconcentration — release and reapply, don't push through.