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

The grey top tube is specifically designed for glucose testing, which is a crucial aspect of diagnosing and managing diabetes and other metabolic conditions. This tube typically contains potassium oxalate as an anticoagulant and sodium fluoride as a preservative. Sodium fluoride is particularly important for glucose testing because it inhibits glycolysis, the process that breaks down glucose in the blood sample. By preventing this breakdown, the grey top tube ensures that accurate glucose levels are measured.

In contrast, other tubes serve different purposes. The green top tube is often used for tests requiring heparin, such as certain chemistry assays, while the blue top tube is primarily utilized for coagulation tests due to the presence of sodium citrate. The purple top tube, which contains EDTA as an anticoagulant, is generally used for complete blood counts and other hematological tests. Thus, the grey top tube is the optimal choice for glucose testing, ensuring that the results are both accurate and reliable.