Partial thromboplastin time (PTT)

Injury	Disease	Nutrition	Poison

Symptoms	Surgery	Test	Special Topic

Overview

Risks

Results

Partial thromboplastin time (PTT)

Alternative Names:

APTT; PTT; Activated partial thromboplastin time
What the risks are:

excessive bleeding
fainting or feeling light-headed
hematoma (blood accumulating under the skin)
infection (a slight risk any time the skin is broken)
multiple punctures to locate veins

Note: this test is often performed on people who may have bleeding problems; if so, the risk of bleeding and hematoma are slightly greater than for people without bleeding problems.
Special considerations:

text continues below

Coagulation (blood clotting) results from a sequence of reactions involving several proteins known as coagulation factors. Some of these factors have other names. For example, Factor I is also called fibrinogen, Factor II is prothrombin, and Factor XII is Hageman factor. The liver produces these proteins and secretes them into the blood. In addition, vitamin K is important to blood clotting because your body converts it into prothrombin.

Some people take warfarin to keep their blood from clotting. Warfarin inhibits prothrombin, thus interrupting the clotting cascade. Because of the link between vitamin K and prothrombin, people who take warfarin need to have consistent levels of vitamin K in their diet, as instructed by their doctor.

Coagulation begins when some of the coagulation factors contact damaged tissue. Each factor reaction triggers the next reaction, in a cascade. The final product of the coagulation cascade is the blood clot.

Factor X can be activated by two separate sequences of chemical reactions. The factors involved in the two sequences are referred to as the intrinsic system and the extrinsic system.

The intrinsic system involves activation of Hageman factor by tissue not normally in contact with blood, followed by sequential activation of factors XI, IX, and X, in the presence of factor VIII.