Which of the following tubes contains anticoagulants?

The light blue tube is specifically designed to contain anticoagulants, namely sodium citrate. This anticoagulant works by binding calcium in the blood, which is essential for the coagulation process. As a result, blood samples collected in a light blue tube are primarily used for tests that require plasma, such as prothrombin time (PT) and activated partial thromboplastin time (aPTT) assays.

In contrast, the red tube does not contain any additives, hence it is considered a serum tube and is used for serum tests where coagulation is a necessary part of the testing process. The tiger top tube, also known as a serum separator tube, contains a gel that separates the serum from the blood cells after centrifugation but does not have anticoagulant properties. The royal blue with a red stripe tube varies in its use; some may or may not contain additives, but the red stripe typically indicates no additives, similar to the red tube. Therefore, the light blue tube is the correct choice as the one that definitively contains an anticoagulant.