Collection Procedures

Introduction

This is the heart of the job and the heart of the exam. More than a third of your questions come from this one domain, and most of them test the same handful of things over and over: the fixed sequence a venipuncture follows from requisition to bandage, which tube is filled in which order and why, where on the arm you are allowed to draw, what size needle at what angle, and how dermal (capillary) puncture differs from venous. Nearly every fact in this chapter traces back to two CLSI standards — GP41 for venous collection and GP42 for capillary collection — and the exam writers know those standards cold. So will you by the end of this chapter.

The reason collection is so heavily weighted is that almost everything that can go wrong with a blood test goes wrong here, at the point of collection, before the specimen ever reaches an instrument. A tube filled out of order, a tourniquet left on too long, a needle too fine for the vein — each of these produces a wrong result that looks perfectly normal on the analyzer. The chemistry is invisibly corrupted. That is why the exam cares less about whether you can name a vein and more about whether you know the sequence and the why behind each step. Learn the reasoning and the sequence stops being a list to memorize and becomes a story that can only run one way.

The venipuncture sequence, start to finish

Every routine venous draw follows one fixed sequence, and a large share of exam items are simply testing whether you know which step comes before which. Here is the whole sequence, in order:

1. Review the requisition. Confirm the ordered tests, the tubes and volumes they require, any fasting or timed-draw instructions, and any special handling — before you go near the patient, because the requisition determines what you carry to the bedside.
2. Identify the patient using two identifiers (Chapter 4 covers this in depth).
3. Perform hand hygiene and put on gloves.
4. Position the arm so it is supported and slopes slightly downward from shoulder to wrist. The downward slope, with the tube always below the site and filling stopper-up, keeps tube contents from flowing backward into the patient's vein (reflux).
5. Apply the tourniquet three to four inches above the intended site.
6. Palpate and select the vein by feel, not by sight.
7. Cleanse the site with 70% isopropyl alcohol and let it air-dry completely.
8. Anchor the vein by pulling the skin taut below the site.
9. Insert the needle, bevel up, at 30 degrees or less.
10. Fill the tubes in the correct order of draw.
11. Release the tourniquet — once the last tube begins filling, and always before the needle comes out.
12. Withdraw the needle and immediately activate the safety device.
13. Hold pressure on the site.
14. Label the tubes — at the bedside, in the patient's presence, before you leave.
15. Dispose of the sharp in the sharps container and complete post-draw care.

Two steps are reversed in almost every set of wrong answers, and you should treat both as reflexes. First, the tourniquet comes off before the needle comes out. Pulling a needle out of a vein that is still pressurized by the tourniquet forces blood into the surrounding tissue and creates a hematoma. Second, labeling happens in front of the patient, not back at the workstation — a tube labeled later at the bench is the oldest route to a mislabeled specimen, which is the single most dangerous error in the laboratory.

Several of the individual steps have specific rules the exam loves to test:

• Requisition first (CLSI GP41). The requisition tells you what to bring. Reading it at the bedside instead of before you gather supplies is how you end up short a tube and having to stick the patient twice.
• Cleanse and let it dry (CLSI GP41). Scrub with 70% isopropyl alcohol for about 30 seconds and let it air-dry completely. Do not fan it, blow on it, or wipe it dry — all three re-contaminate the site. Wet alcohol under the needle also stings the patient and hemolyzes the specimen.
• Anchor below, never above. Pull the skin taut with your thumb one to two inches below the puncture site. Anchoring above the site, or across the needle's path, puts your own finger directly in line with the needle.
• Tourniquet off before the needle out (CLSI GP41). Release it as the final tube fills.
• Pressure, then bandage. Hold firm, direct pressure with the arm straight for at least two minutes — longer for patients on anticoagulants — before you apply gauze and tape. Bending the elbow over a folded gauze pad is a leading cause of bruising, because it does not actually compress the puncture.
• Label in the patient's presence (Joint Commission NPSG.01.01.01). Both pre-labeled tubes (labeled before the draw) and tubes labeled later at the bench are unacceptable.

Key numbers & facts — the venous sequence - Alcohol scrub: 70% isopropyl, about 30 seconds, then air-dry completely — never fan, blow, or wipe. - Anchor 1–2 inches below the site; tourniquet 3–4 inches above the site. - Insert bevel up at 30° or less (10–15° for a winged set in a shallow hand vein). - Tourniquet OFF before the needle is withdrawn — every time. - Hold pressure with the arm straight for at least 2 minutes (longer if anticoagulated). - Label at the bedside, in the patient's presence — never before the draw, never later at the bench. - Activate the safety device immediately as the needle leaves the skin.

Worked example — put the steps in order. A question gives you these four steps out of sequence: (1) release the tourniquet, (2) label the tubes, (3) withdraw the needle, (4) activate the safety device. The correct order is release the tourniquet → withdraw the needle → activate the safety device → label the tubes. The tourniquet always comes off before the needle; the safety device is engaged the instant the needle clears the skin, before anything else is done with it; and labeling is the last of the four, done at the bedside. If an answer choice puts "withdraw the needle" before "release the tourniquet," it is wrong no matter what else it gets right.

Common traps in this section

• Withdrawing the needle before releasing the tourniquet. The most tested reversal in phlebotomy. Tourniquet first.
• Wiping or fanning the alcohol dry. It must air-dry on its own.
• Bending the elbow up over the gauze. Keep the arm straight and apply direct pressure; bending does not compress the site and causes hematomas.
• Labeling at the workstation "to save time." This is how specimens get mislabeled; it is never acceptable.

The order of draw and what each tube serves

If there is one thing on this entire exam you must know perfectly, it is the order of draw. Tubes are filled in a fixed sequence so that additive carried on the needle from one tube cannot contaminate the next test drawn. Get the sequence wrong and you produce results that are precisely, predictably, invisibly wrong.

Memorize the six positions in order, then attach the additive and the tests to each:

1 — Blood culture (sterile) · 2 — Light blue (citrate) · 3 — Red / gold serum · 4 — Green (heparin) · 5 — Lavender / pink (EDTA) · 6 — Gray (fluoride/oxalate).

A classic memory phrase for the tube colors that follow the cultures is "Ladies Really Love Green Lavender Gowns" — Light blue, Red, Light green/green, Lavender, Gray — but the phrase is only a crutch; you must understand the why, because the exam tests the reasoning as often as the sequence.

Here is each position, its additive, its mechanism, and what it serves:

• 1. Blood culture — yellow SPS tube or culture bottles (CLSI GP41). Sterile collections are always drawn first, so that skin flora and tube additives cannot contaminate the culture. The additive sodium polyanethol sulfonate (SPS) inhibits complement, phagocytes, and some antibiotics so bacteria can grow. This is why blood cultures also get the most rigorous skin antisepsis of any draw. When a culture set is collected with a winged (butterfly) set, fill the aerobic bottle first — the air in the tubing goes into the bottle that tolerates it. With a syringe collection, the convention reverses: inoculate the anaerobic bottle first, so no air is introduced into it.
• 2. Light blue — sodium citrate (CLSI H21). Buffered 3.2% sodium citrate binds calcium reversibly and serves the coagulation studies: PT/INR, aPTT, fibrinogen, D-dimer, and factor assays. The 9-to-1 blood-to-additive ratio is built into the tube, so a complete fill is mandatory — a short-filled citrate tube is rejected because the extra citrate throws off the ratio and falsely prolongs the clotting times.
• 3. Red and gold (SST) — clot activator, with or without gel (CLSI GP41). Plain red tubes have no additive or only a silica clot activator; gold or "tiger-top" serum separator tubes (SST) add a thixotropic gel that forms a barrier between cells and serum after spinning. Both produce serum for chemistry panels, serology, hormone levels, and therapeutic drug monitoring.
• 4. Green — heparin. Lithium or sodium heparin inhibits thrombin and yields plasma with no waiting for a clot, which suits stat chemistries, ammonia, and lactate. Use lithium heparin routinely — but switch to sodium heparin when a lithium level is ordered, because lithium heparin would contaminate the very analyte you are measuring.
• 5. Lavender and pink — EDTA (CLSI GP41). K2 or K3 EDTA chelates calcium irreversibly and preserves cell shape, so it serves the hematology tests: CBC, differential, ESR, reticulocyte count, and hemoglobin A1c. Pink-top EDTA is the usual blood-bank tube for type and screen or crossmatch.
• 6. Gray — sodium fluoride with potassium oxalate. Fluoride is an antiglycolytic agent that stops red cells from consuming glucose inside the tube; oxalate is the anticoagulant. Gray tops serve glucose, glucose tolerance testing, lactate, and blood alcohol.

The reason the sequence is fixed is carryover, and the carryover errors are predictable — which is exactly why they are testable. EDTA drawn out of order is the classic villain: EDTA carried into a later tube chelates that specimen's calcium (falsely lowering calcium) and its potassium salt falsely raises potassium. Heparin reaching a coagulation tube invalidates the aPTT. Clot activator carried into a coagulation tube ruins it. Learn the two directions of the EDTA error — calcium down, potassium up — because it appears again and again.

Key numbers & facts — order of draw | Position | Tube color | Additive | Serves | Mechanism | |---|---|---|---|---| | 1 | Yellow (SPS) / culture bottles | SPS | Blood cultures | Sterile; inhibits complement so bacteria grow | | 2 | Light blue | 3.2% sodium citrate | PT/INR, aPTT, fibrinogen, D-dimer | Reversible calcium binding; 9:1 ratio, must fill full | | 3 | Red / gold (SST) | Clot activator ± gel | Chemistry, serology, drug levels (serum) | Clots, then separates | | 4 | Green | Lithium or sodium heparin | Stat chemistry, ammonia, lactate (plasma) | Inhibits thrombin | | 5 | Lavender / pink | K2/K3 EDTA | CBC, ESR, HbA1c; blood bank | Irreversible calcium chelation | | 6 | Gray | Sodium fluoride + K oxalate | Glucose, GTT, lactate, alcohol | Antiglycolytic | - EDTA out of order → calcium falsely LOW, potassium falsely HIGH. Memorize this direction. - Lithium level ordered → use SODIUM heparin (green), not lithium heparin. - Short-filled light blue (citrate) tube → rejected. The 9:1 ratio is fixed.

Worked example — reason through a carryover error. A chemistry panel comes back with a critically high potassium and a low calcium, but the patient has no symptoms and a repeat draw is normal. What happened? The most likely preanalytical cause is that the EDTA (lavender) tube was drawn before the chemistry tube, and EDTA — a potassium salt that chelates calcium — carried over on the needle into the serum tube. The additive did exactly what it is designed to do, just in the wrong tube: it bound the calcium (low result) and contributed its own potassium (high result). The fix is not to re-run the analyzer; it is to redraw in the correct order.

Common traps in this section

• Putting the serum (red/gold) tube before the citrate (light blue) tube. Citrate is position 2, before serum. Only the sterile blood culture comes before citrate.
• Forgetting that a short citrate tube is rejected. Every other tube tolerates a slight underfill; the citrate tube does not, because of the 9:1 ratio.
• Using lithium heparin for a lithium level. Switch to sodium heparin.
• Mixing up the EDTA error direction. Calcium down, potassium up.