Q&A column

Going against a manufacturer’s instructions necessitates that the FDA-approved test be reclassified as a laboratory-developed test. LDTs require extensive additional validation before being used for patient testing.¹ Because a purpose of instrument flags is to prevent errors, such validation is not advisable and may not be possible.

If turnaround time is a concern, the pathologist should consider reporting only the valid parts of the automated test as a preliminary result and following up with a manual differential.

1. Graden KC, Bennett SA, Delaney SR, Gill HE, Willrich MAV. A high-level overview of the regulations surrounding a clinical laboratory and upcoming regulatory challenges for laboratory developed tests. Lab Med. 2021;52(4):315–328.

Chad M. McCall, MD, PhD
Hematopathologist
Clinical Pathologist
Carolinas Pathology Group
Charlotte, NC
Member, CAP Hematology/Clinical Microscopy Committee

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.

1. 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