aPTT — Normal Range & Interpretation
Full name: Activated Partial Thromboplastin Time
The activated partial thromboplastin time (aPTT) measures the integrity of the intrinsic and common coagulation pathways, including factors VIII, IX, XI, and XII. Clinicians use it to monitor unfractionated heparin therapy, screen for bleeding disorders before invasive procedures, and evaluate unexplained bleeding or bruising. A therapeutic aPTT on heparin typically runs 1.5 to 2.5 times the control value.
| Male | Female | Unit | Category |
|---|---|---|---|
| 25–35 | 25–35 | seconds | Coagulation |
Clinical Context
The activated partial thromboplastin time (aPTT) measures the integrity of the intrinsic and common coagulation pathways, including factors VIII, IX, XI, and XII. Clinicians use it to monitor unfractionated heparin therapy, screen for bleeding disorders before invasive procedures, and evaluate unexplained bleeding or bruising. A therapeutic aPTT on heparin typically runs 1.5 to 2.5 times the control value.
Prolonged aPTT results from heparin administration, hemophilia A and B, von Willebrand disease, liver disease, vitamin K deficiency, disseminated intravascular coagulation, and the presence of lupus anticoagulant. A shortened aPTT reflects acute-phase reactions or early DIC with hypercoagulability. NPs order aPTT alongside PT/INR to distinguish intrinsic from extrinsic pathway defects and to guide anticoagulation decisions at the bedside.
On the AANP exam, expect recognition that aPTT monitors heparin while PT/INR monitors warfarin, and that low-molecular-weight heparin does not require routine aPTT monitoring. Expect questions linking prolonged aPTT with normal PT to intrinsic pathway factor deficiencies such as hemophilia, and questions pairing prolongation of both PT and aPTT with liver failure, DIC, or severe vitamin K deficiency. Candidates must also identify when to hold heparin and notify the provider for critically elevated values above 100 seconds.
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