A gel barrier tube is a specialized medical device used for collecting and preparing blood samples for laboratory analysis. It contains a polymer gel designed to physically separate the liquid component of blood from its heavier cellular components. This separation ensures the collected sample is preserved and ready for accurate diagnostic testing, improving efficiency during handling and transport.
Anatomy and Purpose of the Tube
This blood collection tube functions using a vacuum system that draws a precise volume of blood upon needle insertion. Inside, the gel barrier rests at the bottom, along with specific chemical additives depending on the tube’s intended use. The gel itself is an inert, synthetic polymer, often silicone-based, with a density intermediate between the blood cells and the plasma or serum.
These tubes come in two primary variations, each containing a different chemical additive. Serum Separator Tubes (SSTs) contain a clot activator, such as silica particles, which speeds up the natural clotting process. Plasma Separator Tubes (PSTs), conversely, contain an anticoagulant, like lithium heparin, to prevent clotting altogether. The vacuum and pre-measured additives ensure the correct ratio of blood to additive, which is required for reliable test results.
The Dynamic Separation Mechanism
The gel barrier is activated through centrifugation, where the tube is spun at high speeds, typically between 1,000 and 3,000 times the force of gravity. This mechanical force utilizes density differences to stratify blood components into distinct layers. The heaviest components, the red blood cells and the clot, are forced to the bottom.
The polymer gel is a thixotropic substance, meaning its viscosity changes under stress. During high-speed spinning, the gel temporarily liquefies and flows, moving upward through the blood sample. It stops when it reaches a position matching its specific density, settling precisely between the heavier cellular layer and the lighter liquid layer. Once the centrifuge stops, the gel solidifies again, forming a stable, impermeable physical wall that prevents remixing.
Common Uses in Laboratory Testing
Gel barrier tubes are widely used in clinical laboratories because they simplify sample preparation for analysis. The stable gel barrier allows the separated serum or plasma to remain in the primary collection tube for testing, avoiding manual transfer to a different container. This streamlined process reduces contamination risk and improves laboratory efficiency.
Serum Separator Tubes (SSTs) are the preferred choice for a broad range of chemistry and serology tests, including panels that measure liver function, kidney function, cholesterol levels, and hormone concentrations. The clot activator ensures that all clotting factors are consumed, leaving behind pure serum for analysis. Plasma Separator Tubes (PSTs) are used for tests that require plasma, such as certain emergency chemistry panels and therapeutic drug monitoring.