11.1 Procedural Definition: (“What Is This Test About?”)

The activated clotting time (ACT) is a measurement of the activity of the intrinsic and common coagulation pathways. It measures the time from activation of the pathways by introduction of blood into a tube containing clot activator to the formation of fibrin strands that cause the blood to thicken when tilted.

11.2 Procedural Purpose: Why Should I Perform This Test?

Patients that present with evidence of bleeding without previous trauma or prolonged bleeding with trauma should be evaluated for abnormalities in hemostasis. The ACT is especially useful to evaluate patients with evidence of a coagulation factor deficiency, either inherited or acquired. Clinical signs associated with coagulopathies include:

• bruising (ecchymosis)
  
• hematoma formation
  
• body cavity hemorrhage
  
• rebleeding (bleeding that occurs after initial clotting)
  
• excessive bleeding during surgery.

In these patients, a quick assessment of clotting ability is warranted.

The ACT test is a measure of the activity of the coagulation factors in the intrinsic pathway (Factors XII, XI, IX, and VIII) and the common pathway (Factors X, II, XIII, and V). It is much less sensitive than the activated partial thromboplastin time (APTT) and may not be prolonged unless there is a marked decrease in coagulation factor activity. Common coagulation abnormalities that can result in the prolongation of the ACT test include:

• Factor VIII deficiency (Hemophilia A)
  
• disseminated intravascular coagulation (DIC)
  
• Rodenticide poisoning (vitamin K antagonists).

Significant thrombocytopenia will result in a prolongation of the ACT test. A platelet count is advised before performing this test. If the platelet count is <10 000/μl, the ACT time will be affected.

11.3 Equipment

Equipment used for this test include:

• ACT vacutainer blood collection tubes
  
• serum vacutainer blood collection tubes
  
• syringes (3 or 5 ml)
  
• vacutainer needles and sleeve
  
• butterfly catheter
  
• heating block or water bath
  
• stopwatch or watch with a second hand
  
• gloves

11.4 Procedural Steps: How Do I Perform This Test?

• Gather equipment and supplies for performing the test (see Figure 11.1).
  
• Turn on the heating block and heat to 37^°C.
  
• Place the ACT blood collection tube in one of the heating blocks or water baths and preheat the tube at 37°C for 5–10 minutes. This is an essential step. The tubes must be at 37°C when used to allow consistent results.

  

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