What it measures
APTT (activated partial thromboplastin time) is the time, in seconds, that a plasma sample takes to form a clot after the lab adds chemicals that start one. It tests one group of the clotting factors made by the liver. A longer time means the blood is slower to clot in the tube.
Why people test it
- Measured when unexplained bleeding or easy bruising is being looked into.
- Part of a clotting screen with prothrombin time, often before an operation.
- Used in hospital to monitor heparin, a blood-thinning medicine given by drip or injection.
- Checked when lupus anticoagulant or a shortage of a clotting factor, such as in haemophilia, is suspected.
Typical range
Ranges vary by lab, because they depend on the chemicals and machine used. Some labs give the result as a ratio to their own normal time. Your report shows the lab's own range.
Finger-prick or vein?
A vein sample is needed. Clotting tests use a special tube that must be filled to an exact level, and blood from a finger prick starts to clot as it is collected.