American Medical Certification Association (AMCA) Phlebotomy Practice Exam

The red-top tube is used for collecting serum samples because it contains no additives that interfere with the clotting process. This allows the blood to clot fully before the serum is separated by centrifugation. Once the blood clots, the serum can be easily collected without the presence of cells or clotting factors, making this tube ideal for various laboratory tests that require serum analysis.

In contrast, the other tubes serve different purposes. Green-top tubes typically contain heparin as an anticoagulant, which prevents blood from clotting and is used for plasma samples. Lavender-top tubes contain EDTA, another anticoagulant, making them suitable for hematology tests but not for serum collection. Gray-top tubes usually contain sodium fluoride and potassium oxalate and are primarily used for glucose testing, as they help preserve the sample by inhibiting glycolysis. Each type of tube is specifically designed for certain tests and components of blood analysis, which is why the red-top tube is the standard choice for serum samples.