Which of the following types of therapy is monitored by the activated clotting time (act) test?

Does this test have other names?

ACT, activated clotting time

What is this test?

This test measures how long it takes your blood to clot. It's often used to check how well a medicine called heparin is working. Heparin slows the ability of blood to clot, and the ACT test helps your healthcare provider find the right dosage. This test uses whole blood, which is different from the standard tests for coagulation. Those tests use plasma. Plasma is blood that has had the red cells, white cells, and platelets removed. The ACT test is usually used during procedures when results may be needed right away.

Why do I need this test?

You may need this test if you are getting heparin to prevent your blood from clotting during a procedure such as open heart surgery, cardiac catheterization, or kidney dialysis. This test is usually done in the hospital at your bedside.

What other tests might I have along with this test?

You may have other blood tests to measure how quickly your blood clots. A blood test called activated partial thromboplastin time (APTT) is often done as a backup to the results of the ACT test.

What do my test results mean?

Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your healthcare provider.

This test doesn't measure the amount of heparin in your blood. It measures only how long it takes for a blood clot to form. The results are given in the number of seconds:

• 70 to 120 seconds is the usual amount of time for blood to clot without heparin. 

• 180 to 240 seconds is the usual amount of time for blood to clot with heparin. This is called the therapeutic range.

The therapeutic range is usually about double the normal clotting time. It's important to be in this range because if your ACT is too low, you may be in danger of a blood clot forming during a procedure. Some procedures may require an even longer ACT.

If your ACT is too high, you may be in danger of bleeding.

How is this test done?

The test requires a blood sample, which is drawn through a needle from a vein in your arm.

Does this test pose any risks?

Taking a blood sample with a needle carries risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly sore.

What might affect my test results?

Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your healthcare provider.

Other factors that may affect your results include:

• The effects of surgery

• Body temperature

• Other medicines you are taking

• Getting IV (intravenous) fluids, which can dilute your blood

• Platelet counts and platelet function

• Coagulation factor deficiencies

How do I get ready for this test?

You don't need to prepare for this test. But be sure your healthcare provider knows about all medicines, herbs, vitamins, and supplements you are taking. This includes medicines that don't need a prescription and any illegal drugs you may use.

Lab Names

• Activated Clotting Time; Ground Glass Clotting Time; and Whole Blood Activated Clotting Time
• Other names:
  
• Ground glass clotting time
  
•  Whole blood activated clotting time

Description

• Measures the time for whole blood to clot after the addition of particulate activators, which first activates factor XII and measures the intrinsic pathway's ability to begin clot formation.  By checking the blood clotting status with ACT, the response to unfractionated heparin therapy can be easily and rapidly monitored. 
• It is primarily used to measure the anticoagulant effect of unfractionated heparin (UFH) or other direct thrombin inhibitors (DTI) during cardiac angioplasty, hemodialysis, and cardiopulmonary bypass graft (CABG) surgery. 
• It tends to be more accurate than the aPTT when high doses of heparin are used for anticoagulation. 
• It is less expensive and more easily and rapidly performed than the aPTT providing immediate information on to titrate the medications for the clinical situation.

Reference Range

• Normal = 70-120 seconds (some assays will say up to 180 seconds)
• Therapeutic range for anticoagulation =  150-600 seconds & varies with indication
• Note: This will vary according to the indication - see below
  

Indications

• Hemodialysis:  therapeutic range of 132 to 234 seconds.  It can also help guide the use of protamine sulfate needed to reverse the effect.
• PTCA:  HemoTec > 275 to 300 seconds, or Hemochron > 340 to 400 seconds.  
• CABG:  The accepted goal for the ACT is 400-480 seconds.
• Vascular catheterization, hemodialysis, or extracorporeal membrane oxygenation (ECMO):  determine the heparin dose from a standard nomogram adjusted for the patient's baseline ACT.
  
• The modified ACT test requires a smaller-volume blood specimen, automated blood sampling, standardized blood/reagent mixing and faster clotting times results that the conventional ACT.

Clinical Application

For increased levels:

• Patients receiving heparin which binds to antithrombin to inhibit clotting factors mainly of the intrinsic pathway. 
• Patients receiving warfarin (Coumadin) which reduces the functional activation of vitamin K dependent clotting factors
• Cirrhosis which results in decreased production of clotting factors
• A deficiency in clotting factors.
• Lupus anticoagulants against components involved in the activation of the coagulation cascade

Assess the patient to detect possible bleeding including blood in the urine and the presence of bruises, petechiae, and/or low back pain.


For decreased levels:

• Activate of the thrombotic pathways can shorten the ACT.
  

Related Tests

• Partial Thromboplastin Time (PTT)
• Prothrombin Time
  
• Coagulating Factor Concentration

Lab Interactions

The ACT can be affected by several biologic variables, including:  

• Hypothermia
• Hemodilution
• Platelet number & functions
• Factors affecting the pharmacokinetics of heparin (e.g., kidney or liver disease)
• Antithrombin (AT) deficiency
• A partially or completely occluded specimen can increase ACT measurements

Test Tube

• Black top tube containing a particulate activator

Lab Procedure

• If the patient is receiving a continuous heparin drip, the blood sample is obtained from the arm without the intravenous catheter
• Less than 1 ml of blood is collected into a commercial container. 
• The container is placed into a whole blood micro-coagulation analyzer. 
• When a clot has formed, the ACT value is displayed on the machine's panel.
• Apply pressure to the venipuncture site after procedure.  Remember that the bleeding time will be prolonged because of anticoagulation therapy. 
• For clinical significance, the test results must be correlated with the time of the heparin administration.  A clinical flow sheet is used to list the test results with the time and route of heparin administration.

Storage & Handling

• The sample should not be stored.  It should be tested immediately after it has been obtained.

Patient Counseling

• No preparation needed by the patient.

References

• LaGow B et al., eds. PDR Lab Advisor. A Comprehensive Point-of-Care Guide for Over 600 Lab Tests.  First ed. Montvale, NJ: Thomson PDR; 2007.
• Pagana K, Pagana TJ eds. Mosby's Manual of Diagnostic and Laboratory Tests. 5th Ed.  St. Louis, Missouri. 2014.
  
• Olson JD et al. College of American Pathologists Conference XXXI on Laboratory Monitoring of Anticoagulant Therapy.  Laboratory monitoring of unfractionated heparin therapy.  Arch Pathol Lab Med 1998;122(9):782-98.  PMID:  9740136

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