Activated Partial Thromboplastin Time (APTT)

Blood clotting time

The APTT measures how many seconds it takes for the liquid part of your blood (plasma) to form a clot in the laboratory. It checks a group of clotting proteins, called clotting factors, that work together to stop bleeding. It is often done together with a prothrombin time (PT) to screen the whole clotting system, and it is also used to monitor heparin, a blood-thinning injection.

• To look for a cause of easy bruising, nosebleeds or bleeding that is hard to stop
• As a routine check before an operation or procedure
• To monitor treatment with heparin, a blood thinner given by injection
• When a bleeding disorder such as haemophilia runs in the family
• As part of tests for certain antibodies, such as lupus anticoagulant, in people with blood clots or repeated miscarriages

No special preparation is needed, and you can eat and drink as usual. Tell the collector and your doctor if you take any blood thinner, such as heparin or warfarin, because it affects this result. Keep taking your usual medicines unless your doctor says otherwise.

Sample

Blood sample

How it works

A trained collector comes to your home and takes a small blood sample from a vein in your arm. Clotting tests use a special tube that must be filled to the correct level, so the collector takes care to get the amount right. The whole visit takes only a few minutes.

Report

Within 24 hours of collection.

Your report shows your clotting time in seconds next to the laboratory's reference range. A longer time can point to a shortage of a clotting factor, as in haemophilia, liver disease, heparin treatment, or antibodies that interfere with clotting. A slightly short time is not usually a concern on its own. Your doctor will read the result together with your PT, platelet count and history, and may suggest further clotting tests.

One test: Activated Partial Thromboplastin Time (APTT), from one blood sample.