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

In the case of drawing blood for Prothrombin Time (PT) and International Normalized Ratio (INR) tests, the light blue tube should be filled first. This is because the light blue tube contains sodium citrate, which is an anticoagulant that helps preserve the sample for coagulation studies. It is crucial to fill this tube first to minimize any contamination from other additives that might be present in subsequent tubes.

Filling the light blue tube first ensures that there is an accurate measurement of the patient’s clotting time. Adequate filling is also important, as the blood-to-anticoagulant ratio must be correct for reliable test results. If another tube containing different additives, such as those found in the gold, lavender, or green tubes, is filled first, it could affect the accuracy of the PT/INR test by introducing anticoagulants or other substances that may alter the coagulation process.

Proper order of draw minimizes the risk of sample contamination and ensures that the laboratory results will be valid. Understanding this protocol is vital for medical assistants when performing venipunctures and collecting samples for accurate diagnostic testing.