Coagulation
Coagulation laboratory tests
Activated clotting time
Author: Jeremy C. Parsons, M.D.
Last author update: 1 June 2012
Last staff update: 10 September 2020
Copyright: 2002-2023, PathologyOutlines.com, Inc.
PubMed Search: Activated clotting time [title]
Table of Contents
Definition / generalCite this page: Parsons JC. Activated clotting time. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/coagulationACT.html. Accessed June 5th, 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)
