The sensitivity of the ACT test to heparin depends on the method used. The ACT measures the inhibiting effect that heparin has on the body’s clotting system, not the actual level of heparin in the blood. Once the procedure is complete and the patient has been stabilized, heparin doses are typically decreased. (This type of testing is known as point-of-care testing.) ACT testing allows measurement of relatively rapid changes in heparin infusion, helping to achieve and maintain a constant level of anticoagulation throughout the surgical or medical procedure. It can also be done in or near the operating room at intervals during and immediately after surgery. The ACT is a rapid test that can be performed at the patient’s bedside prior to surgery or other medical procedures. The activated clotting time (ACT) is commonly used to monitor treatment with high-dose heparin before, during, and for a short time after medical or surgical procedures that require that blood be prevented from clotting, such as heart bypass surgery, coronary angioplasty, and dialysis. In these cases, the ACT must be used for monitoring. The PTT test involves an in vitro clotting reaction and at high levels of heparin, it will not clot. At this level of anticoagulation, the PTT is no longer clinically useful as a monitoring tool. A high dose of heparin prevents clot formation but leaves the body in a delicate dynamic balance between clotting and bleeding. The blood’s contact with artificial surfaces activates platelets and coagulation, initiating a sequence of steps that results in blood clot formation. This means their blood is filtered and oxygenated outside of the body using mechanical devices. During these operations, the patient’s heart and lungs are often bypassed. High doses of heparin are given, for example, before, during, and for a short time after, open heart surgeries. If there is too much heparin, excessive, even life-threatening, bleeding can occur. If the amount of heparin administered is not enough to inhibit the body’s clotting system, blood clots may form in blood vessels throughout the body. Monitoring is a vital part of the anticoagulation therapy because the blood thinning (anticoagulant) effect of heparin can affect each person a little bit differently. In moderate doses, heparin is used to help prevent and treat inappropriate blood clot formation (thrombosis or thromboembolism) and is monitored using the partial thromboplastin time (PTT) or the heparin anti-factor Xa test.
High doses of heparin may be given during medical or surgical procedures that require that blood be prevented from clotting, such as heart bypass surgery. Heparin is a drug that inhibits blood clotting (anticoagulant) and is usually given through a vein (intravenously, IV), by injection or continuous infusion. The activated clotting time (ACT) is a test that is used primarily to monitor high doses of unfractionated (standard) heparin therapy.
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