What is the additive in a royal blue tube with a red stripe?

The correct choice for the additive in a royal blue tube with a red stripe is "None." These specific tubes are designed to collect serum, meaning they do not contain any additives that would interfere with the tests requiring serum analysis. The lack of additives ensures that the sample can be used for a variety of tests without any factors that could affect the results, such as anticoagulants or preservatives.

In blood collection, additives are used in other tubes to preserve the sample or prevent clotting, but in this case, a tube with no additives is often preferred for specific analyses to ensure clear and unaltered results. For example, tubes that do contain an additive, such as EDTA, Sodium Fluoride, or Potassium Oxalate, would be utilized in different contexts based on the requirements for anticoagulation or preservation.