CPT (Certified Phlebotomy Technician) Practice Exam 2025 – 400 Free Practice Questions to Pass the Exam

The correct chemical additive found in a red tube is silicone, which typically refers to the silicone-coated interior that helps to separate serum from the clot in blood samples. Red top tubes are often used for serum collection because they do not contain any additives that affect the coagulation process or interfere with test results, making them ideal for tests that require serum.

This design allows for the natural clotting of the blood sample, after which the serum can be separated from the clot through centrifugation. The absence of anticoagulants allows for accurate measurement of parameters in serum, which is crucial for various laboratory tests, including metabolic panels and liver function tests.

The other choices represent different types of tubes used for specific tests. EDTA, citrate, and heparin are anticoagulants found in their respective colored tubes, which are designed to prevent clotting and are used for specific tests that require plasma rather than serum.