Hey everyone, it's Sarah with RegisteredNurseRN.com and today we're going to talk about the APTT blood test. And as always, whenever you get done watching this YouTube video, you can access the free quiz that will test you on this content. So let's get started. What is an APTT? Well, this is a blood test used to assess how fast the blood clots.
An APTT stands for activated population. partial thromboplastin time. And how we collect this test is we stick a patient's vein, we remove some blood, put it in a special tube and send it to the lab who will run this test. Now this test is helpful in determining if maybe a patient has a bleeding disorder because it's going to look at specific clotting factors within this coagulation cascade. Also, this test is helpful for monitoring a patient who is on heparin.
And we talked about this in depth in our pharmacology review over heparin. But again, to review, heparin is an indirect thrombin inhibitor. And what did thrombin do again? Thrombin helps play a huge role in that clotting process by turning fibrinogen into fibrin. So once we get fibrin on board, that helps really give our clot form because it's mesh-like strands that allow substances to stick to it.
We get a clot to help treat whatever's going on, usually excessive bleeding. So heparin, what it does is it is going to enhance the activity of a naturally occurring substance in our body called antithrombin 3. And what this is going to do is it's going to prevent the activation of thrombin. So we won't be able to have fibrinogen turn into fibrin.
So we're going to prolong how long it takes for this patient to form a clot. So we're going to prolong this really coagulation cascade. And some Sometimes if they're really wanting to investigate what's going on with this patient, do they have a bleeding disorder?
They're also probably going to order a PT-INR level as well. And we talked about that in the previous video. So let's talk about this coagulation cascade because it's going to help us understand what we're actually looking at in our patient when we're ordering an APTT. So this process is started, let's say whenever a patient has maybe some type of external injury that's going to deplete their vascular system of blood or they have some inside injury within that vascular system that's causing some type of issue and we need a clot there to prevent from depleting that vascular system of blood because if we lose all of our blood in our body we're dead we don't have anything to perfuse our organs and body and we're not going to survive so the coagulation cascade is made up of three pathways we have the intrinsic pathway the extrinsic pathway and the common pathway. And these two pathways, intrinsic and extrinsic, meet together at this common pathway to actually create a clot.
And certain clotting factors, depending on the pathway, will be activated in a certain sequence. So we get clot formation. And an APTT is going to check the intrinsic pathway.
Now the intrinsic pathway is activated when we have internal damage or injury within the body. that vascular system. The extrinsic pathway is activated when we have external injury that's going to deplete our vascular system of blood loss.
Now, whenever we talked about the PTINR, that was what that blood test was checking, that extrinsic and those associated clotting factors. With intrinsic, this is what the PAPTT is checking. So the intrinsic pathway deals with clotting factor 12, 11. 9 and 8. Then it's also going to be looking at the common pathway. So really how the intrinsic pathway and the common pathway are working together. And when we're talking about the common pathway, we're talking about factor 1, 2, 5, and 10. Now let's take what we have learned about the APTT and apply it to what we need to know as the nurse.
And some things we need to know are the normal ranges and how that applies to heparin therapy. So the A-PTT is measured in seconds. And you may be wondering, what's the difference between an A-PTT versus a PTT?
Well, they measure the same thing. They're looking at the intrinsic and the common pathways and how they're working together. But the A-PTT has an activator agent that is used in it that helps speed up the clotting time. So that's why we call it an activated partial thromboplast time, hence why this doesn't have an A in front of it.
So because of that, it's going to give us a more of a narrow range and these ranges vary depending on the lab But generally it's about 30 to 40 seconds as your normal range But let's say your patients on heparin you want them a little bit higher than that, right? Because we want to prolong a clot forming So with heparin therapy you want to commit this number to memory you want them about one and a half to two and a half times the normal range for them to be therapeutic and for a PTT the range is about 60 to 70 seconds. Okay, so that wraps up this review over the APTT blood test.
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