Canadian Society for Medical Laboratory Science (CSMLS) Practice Exam

Which blood collection tube is collected for an INR?

1. Blue

2. Green

3. Lavender/purple

4. Red

The correct answer is: Blue

The blue blood collection tube is specifically designed for coagulation studies, which include the International Normalized Ratio (INR) test. This test is crucial for assessing the blood’s clotting ability, particularly in patients who are on anticoagulant therapy like warfarin. The blue tube contains sodium citrate as an anticoagulant, which works by binding calcium in the blood, preventing clot formation during the collection and processing of the sample. When performing coagulation tests, it is essential to use the correct tube because the presence of additives in other tubes can interfere with the assay results. For example, green tubes, which contain heparin, or lavender/purple tubes, which contain EDTA, are not suitable for INR testing because they are intended for other types of tests such as chemistry or hematology. The red tube, which is plain and contains no additives, could potentially allow clotting to occur, making it unsuitable for coagulation studies as well. Thus, the blue tube is the preferred choice for INR testing, ensuring accurate and reliable results in monitoring a patient’s coagulation status.