Features of Red Top Blood Tube Tube color: Red top blood tubes have a red-colored cap, which helps in easy identification and differentiation from other types of tubes. Tube type: Red top tubes are made of glass or PET, with the cap providing an airtight seal to prevent contamination and maintain sample integrity. Clotting process: After blood collection, red top tubes are inverted several times to mix the blood with the clot activator present on the inner walls of the tube. This initiates the clotting process, and the sample is then left undisturbed to allow complete clot formation. Serum separation: Once the blood has clotted, the tube is centrifuged to separate the serum, which is the liquid portion of the blood without cells or clotting factors. The serum is then transferred to another container for further testing. 100pk