Activated Partial thromboplastin time, APTT

APTT (activated partial thromboplastin time) is the most important indicator reflecting the plasma component of the coagulation-anticoagulation system (CAS).

CAS is a combination of vascular, cellular (platelet), and plasma components necessary to maintain blood in a liquid state, while preventing spontaneous bleeding and stopping them (hemostasis).

If we briefly describe the mechanism of stopping bleeding, it looks like this: the vessel wall is damaged, bleeding begins. First of all, there is a reflex spasm of the vessel. Next, clotting factors are activated, which "attract" platelets to the bleeding site. After the rupture site is clogged with platelet cells, the whole mass begins to be braided with fibrin strands like a grid. Then the platelets secrete substances that compress and seal the entire thrombus so that it clogs the rupture site. The bleeding is stopped, after the vessel is restored, it is necessary to dissolve the thrombus so that it does not come off and clog the lumen of any smaller artery (the cause of the stroke).

The plasma component of hemostasis consists of 3 phases:

I – formation of prothrombinase;

II – thrombin formation;

III – formation of fibrin.

The test reveals plasma defects in the activation of coagulation factor X in the first phase of prothrombin formation. The prolongation of APTT reflects the deficiency of coagulation factors (except VII and XIII), which occurs when they are significantly reduced below 10-25% of normal. A prolonged APTT indicates prolonged clotting time (hypocoagulation).

The test is necessary to monitor the treatment with blood-thinning drugs.

Read also: "Coagulogram and its indicators".