A Vacutainer tube is a specialized, sterile container used to collect and store blood samples for laboratory testing. Although “Vacutainer” is a proprietary brand name, it commonly refers to any closed-system device that uses a vacuum for venipuncture. This standardized method efficiently draws blood directly from a vein into a prepared tube. The system ensures the correct amount of blood is collected and immediately mixed with specific chemicals that preserve the sample’s integrity until analysis.
The Physical Components
The blood collection system is composed of three interconnected parts: the tube, the needle, and the holder. The tube is a sterile cylinder, typically made from glass or shatter-resistant plastic. It is sealed with a color-coded rubber stopper or safety cap, which protects the contents and maintains the internal vacuum.
The collection needle is double-ended, with one end designed for insertion into the patient’s vein. The other, shorter end is encased in a thin rubber sleeve and is intended to pierce the rubber stopper of the tube. This design allows for multiple tubes to be collected during a single venipuncture procedure without blood leaking. The needle screws into a single-use plastic holder, which acts as a stable platform for pushing the tube onto the needle.
How the Vacuum System Works
The functionality of the system is dependent on the pre-measured negative pressure sealed inside the tube. Before use, the tube is evacuated of air, creating a vacuum maintained by the rubber stopper. This vacuum is calibrated to draw an exact volume of blood, ensuring a consistent ratio of blood to the tube’s internal additives.
When the needle is in the vein and the tube is pressed into the holder, the inner needle pierces the rubber stopper. The pressure differential between the vein and the tube causes the blood to be automatically suctioned into the container. The flow stops once the vacuum pressure equalizes with the external pressure, indicating the tube has been filled to its predetermined volume. This closed system prevents the blood sample from being exposed to air or contaminants, which helps maintain the sample’s quality for testing.
Decoding the Color-Coded Tubes
The colored cap on each tube is a universal indicator of the specific chemical additive inside the container. These additives prepare the blood sample for the specific laboratory test requested. Using the wrong color tube can render the sample unusable, potentially leading to inaccurate results.
For instance, the lavender or purple-topped tube contains the anticoagulant Ethylenediaminetetraacetic acid (EDTA). EDTA works by binding to calcium ions in the blood, which prevents clotting. This tube is used primarily for whole blood tests like a Complete Blood Count (CBC).
Conversely, the light blue-topped tube contains sodium citrate, which acts as an anticoagulant and is used for coagulation studies, such as Prothrombin Time (PT). The gold or “tiger top” tube contains a clot activator and a serum separator gel. The clot activator accelerates the natural clotting process, and after centrifugation, the gel forms a physical barrier between the separated serum and the blood cells, making the serum ideal for chemistry and hormone tests.