aPTT (Activated Partial Thromboplastin Time)
Definition
Measures the number of seconds it takes for blood to clot. Unlike PT, it evaluates a different subset of clotting factors and their function.
Purpose
Investigates the cause of unexplained bruising or bleeding. Monitors patients receiving heparin therapy. Assesses bleeding risk in high-risk individuals. Detects clotting problems associated with autoimmune conditions such as lupus.
Results
- Prolonged clotting time, hemophilia, liver disease, vitamin K deficiency, inherited bleeding disorders, or excessive heparin level
- Faster than normal clotting, early DIC, high clotting factors, or advanced-stage cancer
Normal Values
Laboratory-specific.
Risks and Limitations
Clotting in the test tube may differ from clotting in the body. Autoimmune diseases can produce falsely prolonged times that do not reflect true bleeding tendency. Abnormal results require additional testing to confirm.