Chapter 1 of 535% of exam
Collection Procedures
The largest domain on the CPT exam: how a venipuncture runs from requisition to bandage, which tube is filled in which order and why, and how dermal puncture differs. Nearly every fact here traces back to the CLSI venous and capillary collection standards.
The venipuncture sequence, start to finish
Every routine venous draw follows one fixed sequence, and exam items are usually testing whether you know which step comes before which. Review the requisition, identify the patient, sanitize and glove, position the arm, apply the tourniquet, palpate and select the vein, cleanse, anchor, insert bevel up, fill tubes in order, release the tourniquet, withdraw, activate the safety device, hold pressure, then label at the bedside. Two steps are reversed in almost every set of wrong answers: the tourniquet comes off before the needle comes out, and labeling happens in front of the patient rather than back at the workstation.
Requisition first
Confirm the ordered tests, the tubes and volumes they require, fasting or timed-draw instructions, and any special handling before you approach the patient, because the requisition determines what you carry to the bedside.
CLSI GP41Cleanse and let it dry
Scrub the site with 70% isopropyl alcohol for about 30 seconds and allow it to air-dry completely; fanning, blowing, or wiping it dry cancels the antisepsis, and wet alcohol under the needle causes stinging and hemolysis.
CLSI GP41Anchor below, never above
Pull the skin taut with your thumb one to two inches below the puncture site; anchoring above or across the needle path puts your own finger in line with the needle.
Tourniquet off before the needle out
Release the tourniquet once the final tube begins filling and always before withdrawing the needle, because pulling a needle out of a pressurized vein forces blood into the tissue and creates a hematoma.
CLSI GP41Pressure, then bandage
Hold firm direct pressure with the arm straight for at least two minutes, and longer for patients on anticoagulants, before applying gauze and tape; bending the elbow over the gauze is a leading cause of bruising.
Label in the patient's presence
Tubes are labeled immediately after collection, at the bedside or chair, before you leave the patient. Pre-labeled tubes and tubes labeled later at the bench are both unacceptable.
The Joint Commission NPSG.01.01.01The order of draw and what each tube serves
Tubes are filled in a fixed sequence so additive carried on the needle cannot alter the next test drawn. Memorize six positions in order, then attach the additive and the panel to each: sterile, citrate, serum, heparin, EDTA, fluoride. Carryover errors are predictable and testable, so EDTA drawn out of order falsely lowers calcium and raises potassium, and heparin reaching a coagulation tube invalidates the aPTT.
1. Blood culture (yellow SPS or culture bottles)
Sterile collections are always drawn first so that skin flora and tube additives cannot contaminate the culture; the additive sodium polyanethol sulfonate inhibits complement, phagocytes, and some antibiotics.
CLSI GP412. Light blue: sodium citrate
Buffered 3.2% sodium citrate binds calcium reversibly and serves PT/INR, aPTT, fibrinogen, D-dimer, and factor assays. The nine-to-one blood-to-additive ratio makes a complete fill mandatory, so a short draw is rejected.
CLSI H213. Red and gold SST: clot activator, with or without gel
Plain red tubes contain no additive or only a silica clot activator; gold or tiger-top serum separator tubes add a thixotropic gel. Both produce serum for chemistry panels, serology, hormone levels, and therapeutic drug monitoring.
CLSI GP414. 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 sodium heparin when a lithium level is ordered.
5. Lavender and pink: EDTA
K2 or K3 EDTA chelates calcium irreversibly and preserves cell shape, so it serves CBC, differential, ESR, reticulocyte count, and hemoglobin A1c. Pink-top EDTA is the usual blood bank tube for type and screen or crossmatch.
CLSI GP416. Gray: sodium fluoride with potassium oxalate
Fluoride is an antiglycolytic agent that stops red cells from consuming glucose in the tube, and oxalate is the anticoagulant. Gray tops serve glucose, glucose tolerance testing, lactate, and blood alcohol.
Site selection, and the arms you must not use
The antecubital fossa is the default region, but within it the veins are ranked, and several sites are off limits regardless of how good the vein feels. Palpate rather than look, because a vein you can feel bouncing back under your fingertip is more reliable than one you can only see. When both arms are unusable, escalate rather than improvise.
Median cubital vein is first choice
It sits centrally in the antecubital fossa, is well anchored by surrounding tissue, is largest and closest to the surface, and is farthest from major nerves and arteries, so it is both the easiest and the safest stick.
CLSI GP41Cephalic vein is second choice
It runs along the lateral or thumb side of the arm and is often the only palpable vein in patients with more subcutaneous tissue, though it tends to roll and needs firm anchoring.
Basilic vein is last resort
It lies on the medial or little-finger side directly over the brachial artery and median nerve, so it carries the highest risk of nerve injury and arterial puncture and is used only after the other two are ruled out.
CLSI GP41Never draw above an infusing IV
Blood drawn upstream of running fluid is diluted and chemically wrong. If no other site exists, have the nurse stop the infusion for at least two minutes, draw below the IV, discard the first 5 mL, and document what was done.
CLSI GP41Restricted arms
Avoid the arm on the side of a mastectomy without provider approval, an arm with a fistula, graft, or vascular access device, and any site with edema, burns, scarring, tattoo over the vein, hematoma, or active infection.
Hand and lower extremity rules
Hand and wrist dorsal veins are acceptable with a 23-gauge winged set at a shallow angle, but the underside of the wrist is never used because of nerve and tendon proximity, and foot or ankle draws require a provider order in most facilities.
Needle gauge, insertion angle, and the one-minute tourniquet
Gauge numbers run backwards, so a larger number means a thinner needle. Matching gauge to vein prevents both collapse and hemolysis, and matching angle to depth prevents going through the far wall. Tourniquet time is one of the most heavily tested numbers on the exam because prolonged constriction changes the result itself, not just the comfort of the draw.
21-gauge is the routine standard
A 21-gauge multisample needle is the default for adult antecubital venipuncture; it fills evacuated tubes at a rate that avoids both hemolysis and vein collapse.
CLSI GP4122 to 23-gauge for small or fragile veins
Use a 22-gauge needle or a 23-gauge winged infusion set for hand veins, pediatric patients, and elderly patients with fragile vessels. Needles thinner than 23-gauge shear red cells and produce hemolyzed specimens.
Insert at 30 degrees or less
Enter bevel up at an angle of 30 degrees or less relative to the skin; a shallower 10 to 15 degrees is used for superficial hand veins with a winged set.
CLSI GP41Tourniquet placement and time
Apply the tourniquet three to four inches above the intended site and keep it on no longer than one minute. If more time is needed, release it, wait two minutes, and reapply.
CLSI GP41No fist pumping
The patient may make a fist once, but vigorous pumping releases potassium and lactate from muscle and falsely elevates potassium, ionized calcium, and lactate results.
CLSI GP41Two attempts, then hand off
Standard practice limits a phlebotomist to two unsuccessful attempts on a patient before notifying a supervisor or another collector, both for patient comfort and to prevent tissue injury.
Dermal puncture and special populations
Capillary blood is a mixture of arterial, venous, and interstitial fluid, so it is not interchangeable with venous blood for every test, and it has its own order of draw. Depth limits exist because the bone lies close under the skin in infants, and puncturing bone risks osteomyelitis. Special populations mostly change the site, the device, and the volume rather than the underlying technique.
Heel stick site and depth
In infants use only the medial or lateral plantar surface of the heel, and never exceed 2.0 mm depth. The posterior curvature of the heel is avoided entirely because the calcaneus lies directly beneath it.
CLSI GP42Heel versus finger by age
The heel is the required capillary site for infants under one year of age; finger puncture is reserved for children old enough to walk and for adults, because an infant fingertip has too little tissue over the bone.
CLSI GP42Finger puncture technique
Use the palmar surface of the distal segment of the third or fourth finger, puncture slightly off center and perpendicular to the fingerprint lines so the drop forms rather than running along a groove, and stay within 2.0 mm depth.
CLSI GP42Discard the first drop, never milk
Wipe away the first drop because it contains excess tissue fluid, and apply only intermittent gentle pressure; squeezing or milking the site dilutes the sample with interstitial fluid and causes hemolysis.
CLSI GP42Capillary order of draw is different
For dermal collections the sequence is blood gas specimens first, then EDTA, then other additive tubes, then serum tubes, so that the platelet-sensitive EDTA specimen is filled before clotting begins in the puncture.
CLSI GP42Warming and newborn screening cards
Warm the site for three to five minutes with a device no hotter than 42 degrees Celsius to increase blood flow. Newborn screening filter paper circles are filled from one side with a single free-flowing drop each, never layered or filled from both sides.
CLSI NBS01Test your knowledge
Practice questions on Collection Procedures