Activated clotting time (ACT), also known as activated coagulation time, is a test of
coagulation
Coagulation, also known as clotting, is the process by which blood changes from a liquid to a gel, forming a thrombus, blood clot. It results in hemostasis, the cessation of blood loss from a damaged vessel, followed by repair. The process of co ...
.
[labtestsonline.org > ACT]
This article was last reviewed on March 20, 2008. This page was last modified on March 30, 2010
The ACT test can be used to monitor anticoagulation effects, such as from high-dose
heparin
Heparin, also known as unfractionated heparin (UFH), is a medication and naturally occurring glycosaminoglycan. Heparin is a blood anticoagulant that increases the activity of antithrombin. It is used in the treatment of myocardial infarction, ...
before, during, and shortly after procedures that require intense
anticoagulant
An anticoagulant, commonly known as a blood thinner, is a chemical substance that prevents or reduces the coagulation of blood, prolonging the clotting time. Some occur naturally in blood-eating animals, such as leeches and mosquitoes, which ...
administration, such as
cardiac bypass,
interventional cardiology
Interventional cardiology is a branch of cardiology that deals specifically with the catheter based treatment of structural heart diseases. Andreas Gruentzig is considered the father of interventional cardiology after the development of angioplast ...
,
thrombolysis
Thrombolysis, also called fibrinolytic therapy, is the breakdown (lysis) of thrombus, blood clots formed in blood vessels, using medication. It is used in ST elevation myocardial infarction, stroke, and in cases of severe venous thromboembolism ( ...
,
extra-corporeal membrane oxygenation (ECMO), and continuous
dialysis
Dialysis may refer to:
* Dialysis (chemistry), a process of separating molecules in solution
**Electrodialysis, used to transport salt ions from one solution to another through an ion-exchange membrane under the influence of an applied electric po ...
.
[ It measures the seconds needed for whole blood to clot upon activation of the intrinsic pathway by the addition of factor XII activators. The clotting time is based on a relative scale and requires a baseline value for comparison due to inconsistencies between the source and formulation of the activator being used. It is usually ordered in situations where the ]partial thromboplastin time
The partial thromboplastin time (PTT), also known as the activated partial thromboplastin time (aPTT or APTT), is a blood test that characterizes coagulation of the blood. A historical name for this measure is the Kaolin-cephalin clotting time ...
(PTT) test may take an excessive amount of time to process or is not clinically useful.[
Prolongation of the ACT may indicate a deficiency in coagulation factors, thrombocytopenia, or platelet dysfunction. Clotting time measurements can be affected by drugs such as ]warfarin
Warfarin, sold under the brand name Coumadin among others. It is used as an anticoagulant, anticoagulant medication. It is commonly used to prevent deep vein thrombosis and pulmonary embolism, and to protect against stroke in people who ha ...
, aprotinin
The drug aprotinin (Trasylol, previously Bayer and now Nordic Group pharmaceuticals), is a small protein bovine pancreatic trypsin inhibitor (BPTI), or basic trypsin inhibitor of bovine pancreas, which is an antifibrinolytic molecule that inhibi ...
, and GpIIb/IIIa inhibitors
In medicine, glycoprotein IIb/IIIa inhibitors, also GpIIb/IIIa inhibitors, is a class of antiplatelet agents.
Several GpIIb/IIIa inhibitors exist:
* abciximab (abcixifiban) (ReoPro)
* eptifibatide (Integrilin)
* tirofiban (Aggrastat)
* roxifi ...
, and physiologic disturbances such as hypothermia
Hypothermia is defined as a body core temperature below in humans. Symptoms depend on the temperature. In mild hypothermia, there is shivering and mental confusion. In moderate hypothermia, shivering stops and confusion increases. In severe ...
, hypervolemia
Hypervolemia, also known as fluid overload, is the medical condition where there is too much fluid in the blood. The opposite condition is hypovolemia, which is too little fluid volume in the blood. Fluid volume excess in the intravascular compa ...
, and hypovolemia
Hypovolemia, also known as volume depletion or volume contraction, is a state of abnormally low extracellular fluid in the body. This may be due to either a loss of both salt and water or a decrease in blood volume. Hypovolemia refers to the loss ...
.
History
The ACT was first introduced by Hattersley in 1966. Previously, to monitor coagulation effects, blood was placed in a glass tube, kept at 37 degrees Celsius, and manually manipulated until the blood was no longer fluid. It fell out of favor to monitor heparin dosing during cardiac surgery because of the dedicated time required. While the glass tube surface activated coagulation, the clotting time could be decreased with the use of other activators like celite
Diatomaceous earth ( ), also known as diatomite ( ), celite, or kieselguhr, is a naturally occurring, soft, siliceous sedimentary rock that can be crumbled into a fine white to off-white powder. It has a particle size ranging from more than 3& ...
and kaolin
Kaolinite ( ; also called kaolin) is a clay mineral, with the chemical composition Al2 Si2 O5( OH)4. It is a layered silicate mineral, with one tetrahedral sheet of silica () linked through oxygen atoms to one octahedral sheet of alumina (). ...
.
Methodology
Typically a sample of blood is put in a vial or cartridge along with coagulation activators. The sample is maintained at a specified temperature, often 37 degrees Celsius. The coagulation end point can be determined by the optical (e.g., increased opacity detected by optical sensor) or mechanical properties (e.g., increased rigidity detected by the displacement of material in the vial) of the clotting blood.
Results
Results can vary based on the equipment and methodology used. For example, systems that do not pre-warm the vial or sample may see increased time to clotting because clotting times increase with temperature.
References
Coagulation system
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