The blue bottle is used for hematology tests involving the clotting system, which require inactivated whole blood for analysis.
A Vacutainer is a blood collection tube (sterile glass or plastic tube) used to collect blood samples for laboratory testing.
These tubes have a closure that is evacuated to create a vacuum inside the tube thereby enabling a predetermined amount of blood to be withdrawn.
3.2% buffered sodium citrate is the anticoagulant used. Sodium citrate binds loosely with free calcium ions to form a calcium citrate complex, thus preventing coagulation of blood. These tubes are used for coagulation assays like prothrombin time (INR) and activated partial thromboplastin time.