Non-vacuum blood collection tubes with sodium heparin and a double cap are used for collecting, transporting, and processing blood samples for plasma or whole blood analysis in clinical laboratories. The sodium heparin acts as an anticoagulant, preventing the blood from clotting and preserving the sample for accurate testing, especially in coagulation-sensitive assays. These tubes are typically made of PET plastic, come with a green cap, and are available in various sizes like 13 x 75 mm.