what test for extrinsic pathway
But in the lab, you can do each pathway separately (the INR, or the PT, measures the extrinsic pathway, and the PTT measures the intrinsic pathway). Extrinsic pathway. If you want to get the extrinsic pathway to run in a test tube, you have to add something extrinsic to the blood. Remember: the extrinsic pathway is kicked off by tissue factor combining with VIIa.