Phlebotomy is the process of drawing blood from a patient for various diagnostic tests, transfusions, or research purposes. Blood collection tubes are designed with specific features, and their distinct colors indicate the presence of unique additives. These additives ensure the integrity of the blood sample for specific laboratory tests. Understanding the role of each tube and its contents is important for accurate and reliable test results.
The Light Blue Tube
The light blue-top tube is designed for coagulation studies, which assess the blood’s ability to clot. This tube contains sodium citrate as its additive, acting as an anticoagulant. Sodium citrate is the preferred anticoagulant for these tests. The precise amount of sodium citrate in the tube is important, maintaining a specific 9:1 ratio of blood to additive. This proportion ensures valid coagulation test results.
How the Additive Works
Sodium citrate acts as an anticoagulant by binding to calcium ions in the blood. Calcium is an ion that helps initiate the blood clotting cascade. By binding these calcium ions, sodium citrate prevents the reactions that lead to blood clot formation within the tube. This mechanism ensures the blood sample remains in a liquid state, allowing for accurate analysis of coagulation factors.
Common Tests Performed
The light blue tube is used for coagulation tests that evaluate the body’s clotting ability. The most common tests include the Prothrombin Time (PT) and the Activated Partial Thromboplastin Time (aPTT). The PT test measures the time it takes for blood plasma to clot and assesses the extrinsic and common pathways of coagulation, often used to monitor anticoagulant medications like warfarin. The aPTT test evaluates the intrinsic and common pathways of the clotting cascade, and it is frequently used to monitor heparin therapy or investigate bleeding disorders. Other tests using the light blue tube include fibrinogen levels, a protein important for clot formation, and D-dimer tests, which detect blood clots.
Ensuring Accurate Results
Proper collection techniques are important for accurate results from light blue-top tubes. Maintaining the precise blood-to-additive ratio is crucial; under-filling or over-filling can lead to inaccurate test outcomes. Under-filled tubes result in an excess of anticoagulant relative to blood, which can falsely prolong clotting times. Conversely, over-filling can dilute the anticoagulant, risking clot formation within the sample or inaccurate results. After collection, gentle inversion of the tube ensures proper mixing of the blood with the sodium citrate without causing hemolysis, which can interfere with test results.