When drawing PT/INR Prothrombin Time, which tube should be filled first?

When drawing specimens for PT/INR (Prothrombin Time/International Normalized Ratio), it's important to ensure that the light blue tube is filled first. This tube contains sodium citrate, which acts as an anticoagulant. The reason for drawing this tube first is to prevent contamination from other additives present in the other types of tubes. If a tube with additives, such as the gold or lavender tubes, is filled first, there is a risk that these additives could interfere with the results of the coagulation tests.

By prioritizing the light blue tube in the order of draw, the integrity of the specimen can be maintained, ensuring accurate and reliable testing. After collecting blood in the light blue tube, other tubes can be drawn in accordance with the recommended order of draw, avoiding any cross-contamination that could affect the results of subsequent tests.