ACTIVATED CLOTTING TIME (ACT)
The activated clotting time (ACT) is a point-of-care test most
commonly used to monitor for heparin effect during cardiovascular
surgery. The test consists of adding whole blood to
a test tube most often containing either diatomaceous earth
(celite) or kaolin. These particulate activators induce thrombus
formation, which is timed. Normal ACT values range
between 80 and 120 seconds.
The ACT test is useful in that it uses whole blood, can
be performed easily at the point of care, and provides results
relatively quickly. It is important to realize, however, that
ACT is a nonspecifi c test of coagulation. That is to say, a
prolonged ACT can be caused by almost anything that
decreases coagulation, not just heparin . While ACT is
most affected by the state of the intrinsic coagulation system,
the extrinsic system and platelet function also play a
role. Therefore, heparin, warfarin, platelet dysfunction,
protamine excess, and hemodilution would all be expected
to increase ACT. Mild hyperthermia would not be expected
to increase ACT, while hypothermia would.
commonly used to monitor for heparin effect during cardiovascular
surgery. The test consists of adding whole blood to
a test tube most often containing either diatomaceous earth
(celite) or kaolin. These particulate activators induce thrombus
formation, which is timed. Normal ACT values range
between 80 and 120 seconds.
The ACT test is useful in that it uses whole blood, can
be performed easily at the point of care, and provides results
relatively quickly. It is important to realize, however, that
ACT is a nonspecifi c test of coagulation. That is to say, a
prolonged ACT can be caused by almost anything that
decreases coagulation, not just heparin . While ACT is
most affected by the state of the intrinsic coagulation system,
the extrinsic system and platelet function also play a
role. Therefore, heparin, warfarin, platelet dysfunction,
protamine excess, and hemodilution would all be expected
to increase ACT. Mild hyperthermia would not be expected
to increase ACT, while hypothermia would.
