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Changes to Heparin Therapeutic Range (aPTT Target) Oct. 2021
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.

UCI Clinical Laboratory will be switching to a new lot of aPTT reagent on Wednesday Oct. 6, 2021. 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) Therapeutic Range
Therapeutic Range
anti-Xa UFH Target
Oct. 6, 2021

ACS/DVT/PE and most indications
0.3 - 0.7 units/ml
60 - 100 seconds
65 - 110 seconds
Stroke (recent ischemic stroke or
hemorrhagic stroke in the last 2 weeks)
0.2 - 0.37 units/ml
50 - 65 seconds
55 - 70 seconds

Please also refer to the Heparin per Pharmacy Protocol via the Hospital SharePoint for additional information:
Heparin per Pharmacy Quick Reference Guide

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

Effective date: Oct. 6, 2021

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: 2 hours
Routine: 24 hours (Specimens received between 7 am to 9 pm will be run as a STAT)
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
Inpatient Pharmacy

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

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