Activated Clotting Time ( ACT): Normal range, Test results and clinical significance by nursesnote

 Activated Clotting Time ( ACT)

Normal Findings

• 70-120 second's 
• Therapeutic range of anticoagulation: 150-600 seconds ( normal ranges and anticoagulation ranges vary according to particular therapy). 

Indications

The ACT is primarily used to measure the anticoagulant effect of heparin or other direct thrombin inhibitors during cardiac angioplasty, hemodialysis, and cardiopulmonary bypass (CPB) surgery. 

Test explanation 

This test measures the time for whole blood to clot after the addition of particulate activators. Like the activated partial thromboplastin time (aPTT), it measures the ability of the intrinsic pathway (reaction 1) to begin clot formation by activating factor Xll. By checking the blood clotting status with ACT, the response to unfractionated heparin therapy can be easily and rapidly monitored.  Equally important is the use of the ACT in determining the appropriate dose of protamine sulfate required to reverse the effect of heparin on completion of surgical procedures and hemodialysis. 

  Both the aPTT and the ACT can be used to monitor heparin therapy in patient on CPB. However, ACT has several advantage over the aPTT. First, the ACT is more accurate than the aPTT when high doses of heparin are used for anticoagulation. This make it especially useful during clinical situation requiring high-dose heparin, such as during CPB when high-dose anticoagulation is necessary at levels 10 times those used for venous thrombosis. The aPTT is not measurable at these high doses. The accepted goal for the ACT is 400-480 seconds during CPB. 

   Second, the ACT is not only less expansive, but it is also more easily and rapidly performed than the aPTT, which is time consuming and requires fall laboratory facilities. The ACT can be performed at the bedside. This provides immediate information on which further therapeutic anticoagulation decisions can be based. The capability to perform the ACT at the "point of care" makes the ACT particularly useful for patients requiring angioplasty, hemodialysis, and CPB. 

 A nomogram adjusted to the patients baseline ACT is often used as a guide to reach the desired level of anticoagulation during these procedures. This same nomogram is used in determining the dose of protamine to be administered to neutralize the heparin when a return to normal coagulation is desired on completion of these procedure.  The ACT is used in determining when it is safe to remove the vascular access after these procedures. The modified ACT test requires a smaller volume blood specimen, automated blood sampling, standardized blood/reagent mixing, and faster clotting time results than the conventional ACT is now being used more frequently. 

Interfering factors 

• The ACT is affected by several biologic variables, including hypothermia, hemodilution, and platelet number and function. 
• Factors affecting the pharmacokinetics of heparin ( e.g.  kidney or liver disease ) and heparin resistance due to antithrombin deficiency and contact factor deficiencies can affect ACT measurements. 
• A partially or completely occluded specimen can increase ACT measurements. 

Procedure and patient care

• Fasting: no
• Blood tube commonly used: verify with lab
• Less than 1 ml of blood is collected into a commercial container. This container is the placed into a whole blood microcoagulation analyzer at the bedside. When a clot is formed, the ACT value is displayed on the machine's panel. 
• If the patient is receiving a continuous heparin drip, the blood sample is obtained from the arm without the intravenous catheter. 
• Remember that the bleeding time will be prolonged because of anticoagulation therapy. 
• Assess the patient to detect possible bleeding. Check for blood in the urine and all other excretions and assess the patient for bruises, petechiae, and low back pain. 

Test results and clinical significance 

Increased levels 

• Heparin administration: Heparin, along with antithrombin III, interrupts in the action of several coagulation proteins ( except factor Vll ). As a result, the intrinsic pathway of coagulation is inhibited. This pathway is measured by the ACT and is therefore prolonged. 
• Clotting factors deficiencies: Deficiencies in any clotting factors associated with the intrinsic pathway will be associated with prolonged ACT. 
• Cirrhosis of liver: coagulation factors are proteins that are synthesized in the liver. Liver pathology there-fore is associated with a reduction in coagulation factors; this prolongs the time required for the reactions of the intrinsic pathway and prolongs the ACT. 
• Warfarin administration: Deficiencies in the vitamin K clotting factors associated with the intrinsic  pathway will cause a prolonged ACT. 
• Lupus inhibitor: Lupus inhibitors are autoantibodies against components involved in the activation of the coagulation cascade and thus prolong the ACT. 

Decreased levels

Thrombosis : in thrombotic syndrome in which secondary hemostasis is inappropriately stimulated, the ACT may be shortened.