MLPAO Specimen Collection and Procurement Questions and Answers 2 — Questions and Answers

Question 1: What is the recommended angle for needle insertion during standard adult antecubital venipuncture?

5-10 degrees
15-30 degrees (Correct answer)
45-60 degrees
90 degrees (perpendicular)

Correct answer: 15-30 degrees

The recommended needle insertion angle for venipuncture is 15-30 degrees (bevel up). This angle provides controlled entry into the vein while minimizing the risk of passing through the posterior vein wall.

Needle insertion at 15-30 degrees (bevel up) is the recommended approach for standard adult antecubital venipuncture. A shallower angle (<15 degrees) risks incomplete penetration or subcutaneous placement. A steeper angle (>30 degrees) increases the risk of puncturing the posterior vein wall or striking structures beneath the vein. For surface veins or patients with shallow veins, angles closer to 15 degrees are used. For deep veins with thick tissue over them, angles up to 30 degrees may be appropriate. Proper angle selection requires visual and tactile assessment of the vein's depth and prominence. CMLTO phlebotomy competency standards require technologists to be proficient in adjusting technique for patient variation.

Question 2: Which vein is considered the preferred primary site for adult venipuncture and why?

Basilic vein — it is the largest and most accessible
Median cubital vein — it is large, well-anchored, and has few nearby nerves and arteries (Correct answer)
Cephalic vein — it is most visible in all patients
Dorsal hand veins — they are the safest and most accessible

Correct answer: Median cubital vein — it is large, well-anchored, and has few nearby nerves and arteries

The median cubital vein is the preferred first-choice venipuncture site because it is typically large, well-supported by subcutaneous tissue, well-anchored, and relatively distant from major arteries and nerves.

The median cubital vein is located in the antecubital fossa of the forearm, connecting the cephalic and basilic veins. It is preferred for several reasons: (1) Large caliber allowing easy blood flow; (2) Well anchored by surrounding connective tissue, reducing rolling; (3) Located away from major arteries (brachial artery runs medially) and nerves; (4) Less painful to access than the basilic vein (fewer nerve endings). The cephalic vein (lateral antecubital) is the second choice — accessible but tends to roll. The basilic vein (medial antecubital) is third choice — larger but closer to the brachial artery and medial cutaneous nerve. Dorsal hand veins are used as alternatives when antecubital veins are not accessible.

Question 3: What action should be taken if a hematoma begins to form during venipuncture?

Continue collection and massage the site to disperse the hematoma
Apply the tourniquet more tightly and continue
Immediately release the tourniquet, withdraw the needle, and apply firm pressure (Correct answer)
Redirect the needle to a different vein in the same arm

Correct answer: Immediately release the tourniquet, withdraw the needle, and apply firm pressure

Hematoma formation indicates blood is entering the tissue rather than the collection tube. The tourniquet must be released and needle withdrawn immediately, followed by firm pressure to prevent further extravasation.

A hematoma during venipuncture indicates that blood is escaping from the vein into surrounding tissue, usually because the needle has gone through both walls of the vein (through-and-through puncture) or has been partially withdrawn while still in the arm. The immediate action is: (1) Release the tourniquet to reduce venous pressure; (2) Remove the needle promptly; (3) Apply firm, constant pressure to the site for at least 2-3 minutes (longer for anticoagulated patients); (4) Keep the arm elevated; (5) Apply ice if swelling is significant. Never continue aspirating when a hematoma is forming as this worsens tissue damage. If recollection is necessary, use a different site. Document the complication.

Question 4: For a glucose tolerance test (GTT), a 75g oral glucose challenge is administered. When is the post-load blood specimen collected for a standard 2-hour OGTT?

30 minutes after glucose ingestion
60 minutes after glucose ingestion
120 minutes (2 hours) after glucose ingestion (Correct answer)
90 minutes after glucose ingestion

Correct answer: 120 minutes (2 hours) after glucose ingestion

The standard 2-hour OGTT (oral glucose tolerance test) requires collection of a blood specimen exactly 120 minutes (2 hours) after the patient finishes drinking the 75g glucose solution.

The 2-hour oral glucose tolerance test (OGTT) is used to diagnose diabetes mellitus, gestational diabetes, and impaired glucose tolerance. Standard protocol: (1) Fasting specimen collected; (2) Patient drinks 75g anhydrous glucose dissolved in 250-300 mL water over 5 minutes; (3) Blood specimen collected exactly 2 hours (120 minutes) after the glucose load begins. Diagnostic thresholds (WHO/Diabetes Canada): Normal: <7.8 mmol/L; Impaired glucose tolerance: 7.8-11.0 mmol/L; Diabetes mellitus: ≥11.1 mmol/L. The patient must remain seated and not eat, drink, or smoke during the 2-hour period. Timing is critical — early or late collection affects clinical interpretation. Specimen processing in fluoride tubes prevents glycolysis.

Question 5: What is the function of lithium heparin in a green-top blood collection tube?

It prevents bacterial growth in the specimen
It chelates calcium to prevent coagulation
It inhibits thrombin and activated factor X to prevent clotting while preserving cellular morphology (Correct answer)
It inhibits glycolysis to preserve glucose levels

Correct answer: It inhibits thrombin and activated factor X to prevent clotting while preserving cellular morphology

Lithium heparin is an anticoagulant that works by potentiating antithrombin III, which inhibits thrombin and factor Xa, preventing clot formation. It preserves plasma in a near-physiological state.

Lithium heparin (used in green-top tubes) is a direct anticoagulant that binds to and activates antithrombin III (AT-III), which then rapidly inhibits thrombin (Factor IIa) and Factor Xa, blocking the coagulation cascade and preventing clot formation. The lithium salt form is used rather than sodium or ammonium heparin to avoid electrolyte interference — lithium doesn't interfere with sodium or potassium measurements. Heparin preserves cells and plasma proteins close to their in vivo state, making it preferred for plasma chemistry testing (electrolytes, enzymes, some hormones). However, heparin cannot be used for coagulation testing (interferes with clotting assays) or blood banking specimens. EDTA (purple top) chelates calcium for hematology.

Question 6: A patient is undergoing therapeutic phlebotomy for hereditary hemochromatosis. What is the standard volume of blood removed per session in adult patients?

100-200 mL
250-350 mL
450-500 mL (Correct answer)
700-900 mL

Correct answer: 450-500 mL

The standard therapeutic phlebotomy volume for hereditary hemochromatosis is 450-500 mL per session (equivalent to a whole blood donation), performed weekly or bi-weekly until iron stores normalize.

Hereditary hemochromatosis is an iron overload disorder (most commonly HFE gene mutations — C282Y/H63D) where excess iron accumulates in organs (liver, heart, pancreas, joints). Treatment is therapeutic phlebotomy: 450-500 mL (equivalent to one whole blood unit) removed weekly or bi-weekly until serum ferritin reaches 50-100 mcg/L and transferrin saturation normalizes (<50%). This may require 1-2 years of weekly phlebotomy to deplete iron stores. Maintenance phlebotomy (every 2-4 months) prevents reaccumulation. Each 450-500 mL phlebotomy removes approximately 200-250 mg of iron. Laboratory monitoring of CBC (to avoid anemia) and ferritin guides the therapeutic schedule. MLTs performing therapeutic phlebotomy must be competent in this procedure.

MLPAO Specimen Collection and Procurement Questions and Answers 2

What is the recommended angle for needle insertion during standard adult antecubital venipuncture?