General Information, Hemostasis/Coagulation

Testing Update: UFH Anti-IIa

Effective January 17, 2024, UFH Anti-IIa testing will be performed at both Corewell Health Reference Laboratory West and Blodgett Immediate Response Laboratory in Grand Rapids.

The Anti-IIa 2 stage heparin assay is a chromogenic assay for measuring the activity of unfractionated heparin.  This method only tests unfractionated heparin.

This heparin assay is a two stage Anti IIa ( 2 Stages Heparin Assay) based on the inhibition of a constant amount of Thrombin (IIa) by the tested heparin in the presence of exogenous antithrombin.


Recommend Anti-IIa testing when patient is transitioning from direct oral anti Xa therapy such as Eliquis, (Apixaban), and Xaralto, (Rivaroxaban) to unfractionated heparin for a duration of 72 hours following last dose.  If renal impairment is noted extend time of use to 96 hours following last dose of direct oral anti Xa.

Test is not indicated if the patient is receiving low molecular weight heparin. This test is not indicated for patients on Argatroban or Dabigatran.



Anti-factor IIa (FIIa) heparin assay for patients on direct factor Xa (FXa) inhibitors


UFH Anti-IIa – Epic Code LAB1231437 – Interface code 1231437 – CPT 85520

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