Coagulation
Coagulation laboratory tests
Activated clotting time

Author: Jeremy Parsons, M.D. (see Authors page)

Revised: 6 May 2016, last major update June 2012

Copyright: (c) 2002-2016, PathologyOutlines.com, Inc.

PubMed Search: Activated clotting time [title]

Table of Contents
Definition / General
Cite this page: Activated clotting time. PathologyOutlines.com website. http://www.pathologyoutlines.com/topic/coagulationACT.html. Accessed December 10th, 2016.
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)