Which color cap indicates a tube containing no additives?

The color cap that indicates a tube containing no additives is red. Red top tubes are specifically designed for serum collection and do not have any substances added to them that would affect the blood sample. This allows for the blood to clot naturally, making it suitable for tests that require serum.

In contrast, other color-coded tubes may contain various additives. For instance, green cap tubes typically contain heparin, which is an anticoagulant that prevents blood from clotting. Gray cap tubes often include sodium fluoride or potassium oxalate, which act as preservatives and also prevent clotting. Yellow cap tubes can contain different additives depending on the specific type, such as ACD (acid-citrate-dextrose) or SPS (sodium polyanethol sulfonate), both of which are used for blood cultures or other specific tests that require anticoagulation.

Understanding the purpose and composition of each tube is crucial for accurate phlebotomy and laboratory results.