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Changes to Heparin Therapeutic Range (aPTT Target)
The activated partial thromboplastin time (aPTT) is commonly used to monitor the anticoagulant effects of unfractionated heparin (UFH). Heparin-responsiveness of aPTT reagents may change from lot to lot and among different reagents used on different instrument platforms.

UC Irvine’s Laboratory will be switching to a new lot of aPTT reagent on Wednesday, June 17, 2020. This new lot of reagent shows a different responsiveness to unfractionated heparin compared to the current lot. Changes to the heparin therapeutic range are shown in the table below:
Unfractionated Heparin (UFH) Goal
Therapeutic Range anti-Xa UFH Target aPTT Target
aPTT Target
most indications
0.3 - 0.7 units/ml 65-110 seconds 70-115 seconds
Stroke (recent ischemic stroke or
hemorrhagic stroke in the last 2 weeks)
0.2 - 0.37 units/ml 55-70 seconds 55-75 seconds

Please also refer to the Heparin per Pharmacy Protocol via the Hospital SharePoint for additional information.

As a reminder, anti-Xa activity assay (lab test code UHEP) is an acceptable alternative method to monitor unfractionated heparin therapy.

Effective date: June 17, 2020

Specimen requirement and testing information:

Specimen: Collect 2.7 mL blood in a light blue-top (3.2% sodium citrate) plastic tube

Test code: PTT

Minimum stability (collection to initiation of testing):
Ambient: 4 hours
Refrigerated: Unacceptable
Frozen: 2 weeks

Turnaround time (TAT):
STAT: 60 minutes
Routine: 2-4 hours
Test set up frequency: Daily

Specimen required: 1.0 mL citrated plasma
Minimum volume: 0.5 mL citrated plasma
Rejection criteria: Specimens that exceed stated stability, unlabeled/mislabeled/mismatched specimens, specimens submitted in leaking containers, clotted, hemolyzed or under-filled tubes, specimens submitted in glass tubes

A summary of all tests offered by our laboratory services can be found here:


Jennifer S. Woo, MD

Parmis Khatibi, PharmD, CACP, CTTS, APh
Anticoagulation Pharmacist Specialist

Edwin S. Monuki, MD, PhD
Department of Pathology & Laboratory Medicine
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