Venipuncture, commonly known as a blood draw or phlebotomy, is a medical procedure involving the puncture of a vein to collect a blood sample. Trained healthcare professionals routinely perform this technique to obtain specimens for laboratory analysis. This analysis provides insight into a patient’s health status, aids in diagnosing conditions, and tracks treatment progress. It is a common, minimally invasive procedure that requires precision to ensure sample integrity and patient comfort.
Preparing the Patient and Site Selection
The process begins with verifying the patient’s identity and the required tests to ensure the samples are correctly associated with the individual and the laboratory requests. The phlebotomist must gather all necessary equipment, which includes sterile needles, the appropriate collection tubes, gauze, a tourniquet, and an antiseptic solution. Proper patient positioning is established, typically with the arm extended downward and straight. This positioning stabilizes the limb and uses gravity to make the veins more prominent.
The tourniquet is applied three to four finger-widths above the chosen site to temporarily restrict venous blood flow, causing the veins to swell. It should not remain in place for longer than one to two minutes, as prolonged application can alter test results and increase patient discomfort. The phlebotomist then palpates the area, often the antecubital fossa, to locate the most suitable vessel. The median cubital vein is the preferred target due to its size, stability, and superficial location, making it an optimal choice.
Once the vein is identified, the puncture site is cleaned using an antiseptic solution, such as a 70% isopropyl alcohol pad. The cleaning motion should move outward in a circular pattern from the center to prevent introducing contaminants. The antiseptic must be allowed to air dry completely. Insufficient drying time reduces effectiveness and can cause a stinging sensation upon needle insertion.
Executing the Needle Insertion and Blood Collection
With the site prepared, the phlebotomist uses their non-dominant hand to anchor the vein firmly just below the puncture point, pulling the skin taut. This action stabilizes the vessel, preventing it from “rolling” or moving away during insertion. The sterile needle is uncapped, and the bevel (the slanted opening at the tip) is oriented to face upward.
The insertion is performed with a smooth, decisive motion at an angle between 15 and 30 degrees relative to the skin surface. A shallow angle is used to enter the vein without passing completely through both walls, which could lead to a hematoma. Once the needle enters the vein’s lumen, a flash of blood in the hub or tubing confirms correct placement.
After confirming location, the needle position is secured while the collection tubes are attached to the holder. Multiple tubes must be collected in a specific sequence, known as the order of draw. This sequence prevents chemical additives from contaminating subsequent samples, which could skew laboratory results. The standard order is:
- Blood culture bottles
- Tubes containing sodium citrate (for coagulation tests)
- Serum tubes
- Heparin tubes
- EDTA tubes
- Tubes with glycolytic inhibitors
Each collection tube must fill completely by the vacuum contained within it to ensure the correct blood-to-additive ratio, especially for tubes containing anticoagulants. If a butterfly needle set is used and a coagulation tube is the first sample, a non-additive “discard tube” must be drawn first. This removes air from the tubing’s dead space, ensuring accurate blood volume in the coagulation tube. As each tube is removed, it is gently inverted the required number of times to mix the blood with the additive, preventing clotting.
Concluding the Draw and Aftercare
The final step before removing the needle is releasing the tourniquet to restore normal blood flow. This reduces pressure in the vein and minimizes the risk of bleeding beneath the skin. The tourniquet should be released while the last collection tube is still filling or immediately after removal, ensuring it is off before the needle is withdrawn. Once collection is complete, the needle is removed swiftly and smoothly, aligning the motion with the angle of insertion.
As the needle is removed, immediate, firm pressure is applied to the puncture site with a clean gauze pad. This direct pressure aids in occluding the hole in the vein wall, facilitating the natural clotting process and significantly minimizing the formation of a hematoma (a localized collection of blood outside the vessel). The phlebotomist then activates the needle’s safety mechanism, if applicable, to shield the tip before disposing of the assembly in a designated puncture-resistant sharps container.
The patient is instructed to maintain pressure on the site for two to three minutes until bleeding has stopped. Bending the arm is discouraged because it may not apply adequate pressure directly over the puncture site. Finally, a bandage is applied, and the patient is advised to avoid strenuous activities or heavy lifting with that arm to prevent reopening the site and causing a bruise.