Which tube should be used for drawing a PT and PTT blood test?

The sodium citrate tube is the appropriate choice for drawing blood for PT (Prothrombin Time) and PTT (Partial Thromboplastin Time) tests because it acts as an anticoagulant, effectively preventing the blood from clotting during the testing process. This is crucial since these tests measure the time it takes for blood to clot, and the presence of clots would interfere with accurate results.

Sodium citrate works by binding calcium ions, which are critical for the clotting process, thus ensuring that the blood remains in a liquid state for analysis. The usual ratio of citrate to blood is 1:9 to ensure optimal performance.

While other tube types, such as EDTA tubes, are used for different types of hematological tests, they can interfere with coagulation testing due to their own mechanisms of action in preventing clotting. Serum separator tubes are used for tests that require serum samples, and heparin tubes, while also anticoagulants, create a different effect in the clotting cascade that could compromise PT and PTT results. Therefore, the sodium citrate tube is the most suitable choice for accurate coagulation testing.