Background:
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
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Therapeutic Range
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anti-Xa UFH Target
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aPTT Target (CURRENT LOT)
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aPTT Target (NEW LOT) EFFECTIVE
Oct. 6, 2021
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ACS/DVT/PE and most indications
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0.3 - 0.7 units/ml
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60 - 100 seconds
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65 - 110 seconds
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Stroke (recent ischemic stroke or
hemorrhagic stroke in the last 2 weeks)
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0.2 - 0.37 units/ml
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50 - 65 seconds
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55 - 70 seconds
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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:
http://www.pathology.uci.edu/services/index.asp
Sincerely,
Jennifer S. Woo, MD
Director
Hematology/Coagulation
Parmis Khatibi, PharmD, CACP, CTTS, APh
Anticoagulation Pharmacist Specialist
Inpatient Pharmacy
Edwin S. Monuki, MD, PhD
Chair
Department of Pathology & Laboratory Medicine
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