From the Research
For bedside clotting time testing, a blue-top sodium citrate tube is the recommended collection container, as it contains 3.2% sodium citrate as an anticoagulant which prevents the blood from clotting during transport and processing. This recommendation is based on the study by 1, which evaluated the effects of 3.2% and 3.8% sodium citrate concentration on routine coagulation testing and found that 3.2% citrate is the preferred concentration. The standard blue-top tube has a 9:1 ratio of blood to anticoagulant, which is critical for accurate coagulation testing. When collecting the sample, the tube should be filled completely to ensure the proper blood-to-anticoagulant ratio. Underfilling can lead to falsely prolonged clotting times due to excess anticoagulant relative to the blood volume. After collection, the tube should be gently inverted 3-4 times to mix the blood with the anticoagulant, but avoid vigorous shaking which can cause hemolysis and affect test results. The sodium citrate works by binding calcium ions in the blood, which are essential for the clotting cascade, thus temporarily preventing coagulation until the laboratory testing begins, at which point calcium is added back to initiate the clotting process.
Some key points to consider when using sodium citrate tubes for bedside clotting time testing include:
- The importance of using the correct concentration of sodium citrate, as studied by 2 and 1
- The need to fill the tube completely to ensure the proper blood-to-anticoagulant ratio, as highlighted by 2
- The potential for underfilling to lead to falsely prolonged clotting times, as noted by 2
- The importance of gentle inversion of the tube to mix the blood with the anticoagulant, without vigorous shaking, as recommended by 3
Overall, the use of a blue-top sodium citrate tube is the recommended approach for bedside clotting time testing, due to its ability to prevent blood clotting during transport and processing, and its critical role in ensuring accurate coagulation test results.