What is the role of thixotropic gel present in some tubes?

Thixotropic gel serves a critical function in laboratory blood collection tubes, specifically in the separation of serum from blood cells after the sample has been centrifuged. This gel is designed to form a barrier between the serum and blood cells by becoming less viscous (or more fluid) when subjected to shear stress, such as during centrifugation. Once the centrifuge stops, the gel reverts to its thicker consistency, effectively creating a physical separation of the serum from the cellular components of the blood. This separation is essential for accurate laboratory analysis, as it ensures that the serum can be tested without contamination from the cells, leading to precise and reliable test results.