A multi-draw needle is a specialized component used in the Evacuated Tube System (ETS), the standard method for collecting blood samples in modern healthcare settings. This double-ended, sterile instrument allows healthcare professionals to collect multiple tubes of blood during a single venipuncture procedure. Its purpose is to safely and efficiently obtain various blood samples for laboratory tests without requiring the needle to be removed and reinserted. This system improves patient comfort by minimizing needle sticks and streamlines the workflow for phlebotomists.
Essential Components of the Collection System
The multi-draw needle operates as part of a closed system designed for safety. This system includes the double-ended needle, a tube holder, and the evacuated collection tubes. The needle has a sharp, beveled tip on the anterior end for vein insertion and a shorter, shielded needle on the posterior end for piercing the tube stopper. This needle is securely screwed into the cylindrical plastic tube holder, also known as a hub or adapter, which serves as a handle for the phlebotomist.
The tube holder firmly grips the needle and provides a standardized connection point for the collection tubes. It is sometimes equipped with a Luer adapter, allowing for secure attachment of different devices, such as winged infusion sets. The final component is the collection tube, a sterile, pre-measured tube sealed with a rubber stopper and containing a precise vacuum. The stopper’s color indicates the specific chemical additive inside, such as an anticoagulant or clot activator, required for different diagnostic tests.
The Mechanism Allowing Multiple Blood Draws
The distinguishing feature of the multi-draw needle is the mechanism that prevents blood leakage when vacuum tubes are switched out. The posterior needle, which faces the tube holder, is covered by a retractable rubber sleeve, often called a non-return valve or sheath. This sleeve is designed to spring back and immediately seal the end of the needle when a collection tube is removed.
When a vacuum tube is pushed into the holder, the posterior needle pierces the tube’s rubber stopper, and the rubber sleeve is momentarily pushed back. This retraction exposes the needle opening, allowing blood to flow into the tube, driven by the internal vacuum pressure. As soon as the filled tube is pulled out, the rubber sleeve instantly slides forward over the needle tip, preventing blood from dripping out. This mechanical seal maintains the system’s sterility and permits the phlebotomist to attach subsequent vacuum tubes without re-puncturing the vein.
Standard Use in Venipuncture
The multi-draw system is the industry standard for venipuncture. The procedure begins with a single insertion of the needle into the patient’s vein at a shallow angle, typically between 15 and 30 degrees. Once blood flow is established, the phlebotomist pushes the first vacuum tube into the holder to initiate the draw.
The vacuum inside the tube ensures a precise volume of blood is drawn, which maintains the proper ratio of blood to the chemical additive, particularly for tests like coagulation studies. After the first tube is filled, it is removed and immediately replaced with the next tube in the required “order of draw.” This method reduces patient discomfort and minimizes the risk of complications like hematoma formation or needlestick injuries for the healthcare worker. The process ensures high-quality samples that are accurately filled and uncontaminated, leading to more reliable laboratory results.