ASCP Orders and Equipment Selection 2 — Questions and Answers
Question 1: Which tube stopper color contains sodium citrate as the anticoagulant and is primarily used for coagulation studies?
- Red
- Light blue (Correct answer)
- Green
- Lavender
Correct answer: Light blue
Light blue-topped tubes contain sodium citrate (3.2%) and are the standard tubes for coagulation testing such as PT and aPTT.
Light blue-topped tubes contain 3.2% sodium citrate, which prevents clotting by binding calcium ions. These tubes are specifically designated for coagulation studies including prothrombin time (PT), activated partial thromboplastin time (aPTT), and fibrinogen assays. The precise ratio of blood to anticoagulant (9:1) is critical for accurate results, so these tubes must be filled to the designated volume.
Question 2: A phlebotomist needs to collect blood for a blood gas analysis. Which of the following syringes or tubes should be selected?
- Lavender-topped tube
- Gray-topped tube
- Heparinized syringe (Correct answer)
- Yellow-topped SPS tube
Correct answer: Heparinized syringe
Arterial blood gas (ABG) specimens are collected using heparinized syringes to prevent clotting while not interfering with pH or gas measurements.
Blood gas analysis requires a heparinized syringe because lithium or sodium heparin prevents clotting without significantly altering pH, pCO2, or pO2 measurements. The specimen must be collected anaerobically to prevent atmospheric gas contamination. After collection, air bubbles must be expelled, the syringe capped, and the specimen placed on ice for transport to maintain specimen integrity.
Question 3: When using a winged blood collection (butterfly) set, what is the first tube in the order of draw if coagulation tests are ordered?
- Light blue top
- A discard tube (Correct answer)
- Lavender top
- Red top
Correct answer: A discard tube
With butterfly sets, a discard tube must be drawn first to fill the dead space in the tubing and prevent short-filling the coagulation tube, which would alter the blood-to-anticoagulant ratio.
Butterfly (winged infusion) sets contain a length of tubing that holds approximately 0.5 mL of air (dead space). If a light blue coagulation tube is drawn first, the dead space causes underfilling, altering the critical 9:1 blood-to-citrate ratio. To prevent this, a discard tube (any non-additive or citrate tube) is drawn first to purge the dead space. Only then should the light blue tube be collected to ensure accurate coagulation test results.
Question 4: Which needle gauge is most commonly used for routine adult venipuncture?
- 18 gauge
- 21 gauge (Correct answer)
- 25 gauge
- 27 gauge
Correct answer: 21 gauge
A 21-gauge needle is standard for routine adult venipuncture, providing an adequate flow rate while minimizing discomfort and hemolysis risk.
The 21-gauge needle is the most commonly used for routine adult venipuncture because it balances adequate blood flow with patient comfort. Larger gauges (18G) may cause more pain and are typically reserved for blood bank donations. Smaller gauges (23G, 25G) are used for pediatric or difficult-vein patients but increase the risk of hemolysis due to the narrower lumen.
Question 5: What is the purpose of the rubber sleeve inside an evacuated tube holder?
- To prevent needle stick injuries
- To maintain vacuum in the tube after needle insertion
- To prevent blood from leaking when changing tubes (Correct answer)
- To make the holder more comfortable to grip
Correct answer: To prevent blood from leaking when changing tubes
The rubber sleeve in the tube holder covers the internal needle and prevents blood from leaking into the holder when tubes are removed and exchanged during multi-tube collection.
The rubber sleeve (also called the internal sheath) covers the posterior (internal) needle of the evacuated tube system. When a tube is pushed onto the needle, blood flows into the tube. When the tube is removed, the rubber sleeve retracts over the needle opening, preventing blood from dripping into the holder between tube changes. This self-sealing mechanism allows multiple tubes to be collected with a single venipuncture while maintaining a clean, controlled system.
Question 6: Which collection device is most appropriate for a pediatric patient requiring a small blood volume from a hand vein?
- Standard evacuated tube system with 21-gauge needle
- Syringe with 18-gauge needle
- Winged infusion set (butterfly) with 23-gauge needle (Correct answer)
- Capillary tube with lancet
Correct answer: Winged infusion set (butterfly) with 23-gauge needle
A winged infusion (butterfly) set with a 23-gauge needle is ideal for small or fragile veins such as those in the hand of a pediatric patient.
Winged infusion sets (butterfly needles) are the preferred choice for pediatric patients, elderly patients, or anyone with small, fragile, or rolling veins. The 23-gauge needle is small enough to access hand veins without collapsing them, and the flexible tubing reduces movement at the insertion site. The wings provide stability and control during insertion. For very small volumes, the butterfly can be attached to a syringe for manual aspiration rather than using the vacuum of evacuated tubes, which could collapse small veins.
ASCP Orders and Equipment Selection 2
Which tube stopper color contains sodium citrate as the anticoagulant and is primarily used for coagulation studies?