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Home :: Activated clotting time

Activated Clotting Time

Activated clotting time, or automated coagulation time (ACT), measures whole blood clotting time. This test is commonly performed during procedures that require extra corporeal circulation, such as cardiopulmonary by­ pass, ultra filtration, hemodialysis, and extra corporeal membrane oxygenation (ECMO).

Purpose

  • To monitor the effect of heparin
  • To monitor the effect of protamine sulfate in heparin neutralization
  • To detect severe deficiencies in clotting factors (except factor VII)

Patient preparation

  • Explain to the patient that this test is used to monitor the effect of heparin on the blood's ability to coagulate.
  • Tell him that the test requires a blood sample, which is usually drawn from an existing vascular access site; therefore, no venipuncture will be needed.
  • Explain who will perform the test and that the test is Usually done at the bedside.
  • Explain that two blood samples will be drawn. The first one will be discarded so that any heparin in the tubing doesn't interfere with the results.
  • If the sample is drawn from a line with a continuous infusion, stop the infusion before drawing the sample.

Procedure and posttest care

  • Withdraw 5 to 10 ml of blood from the line and discard it.
  • Withdraw a clean sample of blood into the special tube containing celite provided with the activated clotting time unit.
  • Activate the activated clotting time unit and wait for the signal to insert the signal to insert the tube.
  • Flush the vascular access site according to your facility's protocol.
Precautions
  • Guard against contamination with heparin if drawn from an access site containing heparin.

Reference values

In a non-anticoagulated patient, normal activated clotting time is 107 seconds plus or minus 13 seconds. During cardiopulmonary bypass, heparin is titrated to maintain an activated clotting time between 400 and 600 seconds. During ECMO, heparin is titrated to maintain the activated clotting time between 220 and 260 seconds.

Interfering factors

  • Failure to fill the collection tube completely, to use the proper anticoagulant, to adequately mix the sample and the anticoagulant, or to send the sample to the laboratory immediately or place it on ice.
  • Hemolysis due to rough handling of the sample or to excessive probing at the venipuncture site.
  • Failure to draw at least 5 ml waste to avoid sample contamination when drawing sample from a venous access device that's used for heparin infusion.

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