Library · Test
Partial thromboplastin time
Make it clearer
The partial thromboplastin time measures something very specific: how many seconds it takes a person's blood to form a clot. That number is used to assess the activity of the intrinsic pathway of the coagulation cascade, one of the routes by which the body builds a clot, a reaction that activates one factor after another in a chain.
The procedure has a part that seems contradictory. Blood is collected in a tube containing citrate, almost always with a light blue top, and citrate traps calcium, which is an indispensable part of clotting. So the sample is first kept from clotting. Then, in the laboratory, the plasma, which is the liquid part of the blood, is separated out, and calcium and activating substances are added back to it so that the intrinsic pathway starts right there, on the clock. Calcium is removed to put clotting on pause and added back so it can be measured.
One clarification that prevents misunderstandings: this test examines the function of every clotting factor but two, factor VII and factor XIII, which is the stabilizer of fibrin.
In brief
The partial thromboplastin time is the number of seconds it takes blood to form a clot, and it measures the intrinsic pathway of coagulation.
The sample is collected in a citrate tube, which traps calcium and keeps the blood from clotting; in the lab, calcium and activators are added back to the plasma to start that pathway.
The lab removes calcium to put clotting on pause, then adds it back to start the clock.
It assesses every clotting factor except factor VII and factor XIII.
Sources (1)
- National Center for Biotechnology Information, StatPearls PublishingPartial Thromboplastin Time, StatPearlsPublished
This page explains the topic in general terms; it does not tell anyone what treatment to follow.
Updated