RMA Venipuncture and Phlebotomy 1 — Questions and Answers
Question 1: Which vein is most commonly used for routine venipuncture in adults?
- Cephalic vein
- Median cubital vein (Correct answer)
- Basilic vein
- Femoral vein
Correct answer: Median cubital vein
The median cubital vein, located in the antecubital fossa (the inner elbow), is the most commonly used vein for routine venipuncture because it is large, superficial, and well-anchored.
The median cubital vein is preferred for venipuncture because it is typically the largest and most stable vein in the antecubital area, making it easier to access and less prone to rolling or collapsing. The cephalic vein is an acceptable second choice on the lateral (thumb) side of the arm, while the basilic vein on the medial side is used less frequently because it is prone to rolling and lies near the brachial artery and median nerve. Medical assistants performing venipuncture must be skilled at locating and accessing appropriate veins safely.
Question 2: What is the purpose of applying a tourniquet before venipuncture?
- To prevent bleeding after the needle is removed
- To dilate the veins and make them easier to access (Correct answer)
- To numb the skin before needle insertion
- To prevent the patient from moving during the procedure
Correct answer: To dilate the veins and make them easier to access
A tourniquet is applied proximal to the venipuncture site to temporarily restrict venous blood flow, causing veins to distend (enlarge) and become more visible and palpable.
When a tourniquet is applied to the upper arm, it creates enough pressure to obstruct venous return while allowing arterial blood to continue flowing into the arm. This causes blood to accumulate in the veins, making them engorge and rise closer to the skin surface. The tourniquet should be applied 3–4 inches above the venipuncture site and should not remain in place for more than one minute to avoid hemoconcentration, which can falsely elevate certain lab values. Medical assistants must release the tourniquet before withdrawing the needle to prevent hematoma formation.
Question 3: In the correct order of draw for multiple tube collection, which tube is collected FIRST?
- EDTA (lavender top)
- Sodium citrate (light blue top) (Correct answer)
- SST/serum separator (gold or red/gray top)
- Heparin (green top)
Correct answer: Sodium citrate (light blue top)
In the order of draw for multiple tubes, the light blue top (sodium citrate) tube for coagulation studies is drawn first after any discard tube to prevent contamination from additives in other tubes.
The Clinical and Laboratory Standards Institute (CLSI) order of draw is: blood culture bottles first, then sterile tubes, light blue (sodium citrate for coagulation studies), red or gold (no additive or SST), green (heparin), lavender/pink (EDTA), and gray (fluoride/oxalate for glucose). The light blue top comes early in the order because sodium citrate-based coagulation tests are highly sensitive to contamination from other tube additives. The ratio of blood to citrate (9:1) must be exact, so it is also critical that the tube be filled to the correct level. Medical assistants must memorize and follow the correct order of draw.
Question 4: What does the term 'hematoma' refer to in the context of phlebotomy?
- A condition where the needle enters an artery instead of a vein
- A collection of blood that escapes from a vessel into surrounding tissue (Correct answer)
- Hemolysis of red blood cells in the collection tube
- Fainting caused by the sight of blood during a blood draw
Correct answer: A collection of blood that escapes from a vessel into surrounding tissue
A hematoma is a localized swelling caused by blood leaking from a punctured vessel into the surrounding tissue, forming a bruise-like mass under the skin.
A hematoma is one of the most common complications of venipuncture and occurs when blood leaks out of the vessel into the surrounding tissue. Causes include: the needle bevel not being fully inside the vein, excessive probing, removing the needle before releasing the tourniquet, or insufficient pressure applied after withdrawal. To prevent hematoma formation, medical assistants should release the tourniquet before removing the needle, apply firm pressure for at least 3–5 minutes (longer for patients on anticoagulants), and avoid excessive needle movement during the draw.
Question 5: Which color top tube is used to collect blood for a complete blood count (CBC)?
- Red top (no additive)
- Light blue top (sodium citrate)
- Lavender top (EDTA) (Correct answer)
- Green top (lithium heparin)
Correct answer: Lavender top (EDTA)
The lavender top tube contains EDTA (ethylenediaminetetraacetic acid), an anticoagulant that preserves blood cell morphology, making it the standard tube for CBCs and other hematology tests.
EDTA (ethylenediaminetetraacetic acid) is the anticoagulant in lavender (or purple) top tubes. EDTA prevents clotting by binding calcium ions, which are necessary for the coagulation cascade. Because EDTA preserves cell size, shape, and counts, it is the preferred additive for hematology tests including the CBC, differential, platelet count, erythrocyte sedimentation rate (ESR), and hemoglobin A1c. After collection, lavender top tubes must be gently inverted 8–10 times to mix the blood with the additive. Medical assistants routinely collect lavender top tubes for a wide variety of common laboratory tests.
Question 6: If a patient is on anticoagulant therapy such as warfarin, what special consideration should the medical assistant take after venipuncture?
- Use a larger gauge needle to reduce the number of puncture attempts
- Apply pressure to the site for a longer duration to prevent excessive bleeding (Correct answer)
- Avoid using a tourniquet to prevent bruising
- Collect the blood sample in a red top tube only
Correct answer: Apply pressure to the site for a longer duration to prevent excessive bleeding
Patients on anticoagulant therapy have impaired clotting ability, so the medical assistant should apply firm pressure for an extended period (5–10 minutes or until bleeding stops) to prevent hematoma or excessive bleeding.
Anticoagulant medications such as warfarin (Coumadin), heparin, aspirin, clopidogrel, or newer anticoagulants like rivaroxaban and apixaban interfere with the body's ability to form blood clots. After venipuncture in these patients, medical assistants must apply firm, direct pressure for a prolonged period — typically 5 to 10 minutes — and should not release pressure prematurely to check the site. A pressure bandage can be applied if needed. These patients should also be warned not to rub the site and to watch for signs of excessive bruising or bleeding.
RMA Venipuncture and Phlebotomy 1
Which vein is most commonly used for routine venipuncture in adults?