Q. How useful is an APTT value if the value falls below the reference interval?
A. Any abnormal activated partial thromboplastin time, even one that is accelerated or shortened to below a laboratory’s reference range, is potentially useful. An accelerated APTT can be due to sample collection (artificial activation of clot formation), a hemolyzed sample (when using mechanical clot detection), overt or non-overt disseminated intravascular coagulation (in vivo activation of clot formation), and elevated factor VIII levels.1
That said, APTT tests are usually performed for the initial workup of suspected bleeding disorders, for perioperative testing, and to monitor unfractionated heparin therapy—all of which would typically yield normal or prolonged rather than accelerated APTT results.
The usefulness of a particular APTT result (accelerated or prolonged) should be assessed in the context of the specific clinical scenario.
- Bennett ST, Lehman CM, Rodgers GM. Laboratory Hemostasis: A Practical Guide for Pathologists. 2nd ed. Springer International Publishing; 2015.
Clarence Chan, MD, PhD
Fellow, Clinical Chemistry
Department of Pathology
University of Chicago
Chicago, Ill.
Junior Member, CAP Hemostasis and Thrombosis Committee
Jacob Ritter, MD
Post-graduate Year-four Pathology Resident
Department of Pathology and Laboratory Medicine
UT Health San Antonio Long School of Medicine
San Antonio, Tex.
Junior Member, CAP Hemostasis and Thrombosis Committee
Editor: Frederick L. Kiechle, MD, PhD
Published: October 2022
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