Coagulation laboratory tests

Activated clotting time

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PubMed Search: Activated clotting time [title]

Jeremy C. Parsons, M.D.
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Table of Contents
Definition / general
Cite this page: Parsons JC. Activated clotting time. website. Accessed September 25th, 2023.
Definition / general
  • Whole blood clotting assay, performed at point of case, including operating room or catheterization lab (Am J Clin Pathol 2011;135:741), to monitor high - dose heparin anticoagulation (cardiopulmonary bypass surgery) or to immediately measure heparin (ECMO, hemodialysis, cardiac catheterization)

  • Note: test is necessary for high - dose heparin monitoring because PTT is often unclottable at very high heparin levels

  • Whole blood is collected into tube with celite (diatomaceous earth), kaolin, glass particles or other activator of intrinsic pathway
  • Tube may need to be shaken to disperse the activator
  • Tube is monitored by instrument that records time until clot is formed
  • Do not collect blood from line containing heparin
  • Target reference range depends on the method: usually 70 - 180 seconds, 400+ seconds for cardiopulmonary bypass operations
  • Does not correlate well with PTT but heparin level can be measured using an anti - Xa assay
  • Affected by platelet count and function, lupus anticoagulant, factor deficiencies, patient and ambient temperature, hemodilution, aprotinin (reversible platelet inhibitor that prolongs elite - based tests)
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