This review will highlight the main concepts you need to know about the aPTT test for exams!
The aPTT is a helpful test for assessing the coagulation process. As the nurse you want to know the normal range, what the test assesses, how it’s used to monitor Heparin therapy, and the nurse’s role.
Don’t forget to take the quiz on PT/INR vs. aPTT after reviewing this material.
aPTT Blood Test Review
What’s an aPTT?
An aPTT is a blood test used to see how fast the blood clots. aPTT stands for activated partial thromboplastin time.
To obtain an aPTT, blood will be withdrawn from a vein with a needle, collected in a special vial, and sent to the lab. Then the lab will report the lab result back to you.
The aPTT is helpful in detecting bleeding disorders and monitoring Heparin therapy because it assesses how well the coagulation cascade works. Also, it is sometimes ordered with a PT/INR (which we talked about in the previous review).
Heparin works by enhancing the activity of antithrombin III (a natural substance in our body). This substance inactivates enzymes that play a role in the clotting process.
When it is activated (antithrombin III) it will prevent the activation of thrombin (which converts fibrinogen to fibrin).
The coagulation cascade is a process made up of 3 pathways that leads to the formation of a clot. This is beneficial when injury has occurred that could result in blood loss from the vascular system.
For example, when injury happens (whether it’s an external or internal injury), platelets arrive to the scene and this causes clotting factors to be activated in a specific order from specific pathways of the coagulation cascade. The end result will be that a clot forms and this will help prevent excessive bleeding.
The coagulation cascade includes 3 pathways that lead to the formation of a clot:
- extrinsic pathway: it is activated when there is external injury that results in blood loss to the vascular system.
- intrinsic pathway: it is activated when there is internal injury within the vascular system.
- common pathway: this is where the extrinsic and intrinsic pathway meet to form a clot.
*Each pathway has specific clotting factors that work to form a clot. There are approximately 13 clotting factors.
The aPTT assesses the INTRINSIC and COMMON pathways. Therefore, it checks clotting factors: I, II, V, X (clotting factors of the common pathways), and XII, XI, IX, VIII (clotting factors of the intrinsic pathway).
Key Concepts to Remember about the aPTT
- The aPTT test tells us about how well the intrinsic and common pathway work together to create a clot based on the clotting factors they use.
- It’s measured in seconds.
- The normal range measurement varies among labs because they use different testing agents.
- Normal range for an aPTT: 30-40 seconds (approximate)… results higher than this means the patient has a prolonged time forming a clot.
- aPTT vs PTT? It measures the same thing, but an activator agent is added to the aPTT to speed up the clotting time, which makes the results have a smaller range compared to the PTT.
- Normal range for PTT: 60-70 seconds (approximate)
- The aPTT is measured for patients on Heparin because it more sensitive.
- Heparin therapeutic goal is 1.5 – 2.5 times the normal value range.
You may be interested in Labs to Know for NCLEX Review.
- Food and Drug administration. (2017). Heparin Sodium, for intravenous use Ebook]. Retrieved from https://www.accessdata.fda.gov/drugsatfda_docs/label/2017/017029s140lbl.pdf