What Does APTT Mean on a Blood Test?

What it means

APTT stands for activated partial thromboplastin time. The lab adds chemicals to a tube of your blood plasma that start the clotting process and times how long a clot takes to form. It checks one group of clotting factors, the proteins that work in a chain to stop bleeding.

Doctors order APTT before some operations, when someone bruises or bleeds easily, when a clotting disorder runs in the family, and to monitor people given heparin through a drip. A longer time than the lab's range means the blood took longer than usual to clot in the tube. Some reports also print an "APTT ratio", which compares your time with a standard.

APTT and PT (or INR) are often printed side by side but test different parts of the clotting chain. PT and INR are mainly used to monitor warfarin, while APTT is the one more often used for heparin.

Where you may see it

• Clotting or coagulation screens printed with PT, INR and fibrinogen
• Pre-operative blood tests
• Hospital results for people on heparin given through a drip
• Investigations for easy bruising or a family history of bleeding disorders