he aPTT test is a blood test that measures how long it takes your blood to form a clot. It evaluates the function of certain clotting factors involved in the body’s intrinsic and common coagulation pathways.

What the aPTT test measures

aPTT evaluates the activity of several clotting factors, including:

• Factor VIII

• Factor IX

• Factor XI

• Factor XII

• Other factors involved in the clotting process

What an aPTT test can help detect

An abnormal aPTT result may indicate problems with blood clotting, including:

A prolonged (longer) aPTT may be associated with:

• Hemophilia or other clotting factor deficiencies

• Certain autoimmune conditions (such as lupus anticoagulant)

• Liver disease (because the liver produces many clotting factors)

• Vitamin K-related clotting problems (in some cases)

• Disseminated intravascular coagulation (DIC)

• The effect of blood-thinning medications, especially heparin

A shortened (faster) aPTT may be associated with:

• Increased clotting tendency in some situations

• Inflammation or elevated clotting factors

• Certain technical or sample-related factors

Why the aPTT test is ordered

Healthcare providers may order an aPTT test to:

• Evaluate unexplained bleeding or bruising

• Investigate abnormal bleeding before surgery

• Monitor unfractionated heparin therapy

• Help diagnose bleeding disorders

• Evaluate abnormal results from other coagulation tests

aPTT vs. PT/INR

• aPTT: Evaluates the intrinsic and common clotting pathways; commonly used to monitor heparin therapy.

• PT/INR (Prothrombin Time/International Normalized Ratio): Evaluates the extrinsic and common pathways; commonly used to monitor warfarin therapy and assess clotting function.