Anti-Xa Heparin Assay: Antithrombin in the Reagent?

A new question from Kim Kinney at Clarian

Hi George,

We are looking at switching our heparin assay from a two stage kit (antithrombin [ATIII] reagent included) to one that has no antithrombin and relies upon patient antithrombin. We are facing re-establishing our PTT therapeutic range and wondered how this will impact the therapeutic range and how to address the issue of notifying clinicians since their heparin levels may change.

Thanks, Kim

Hi, Kim. I’m going to want to send your question to a couple of distributors, who may have calibration information they are willing to share. I’m quite certain that when you change you will have to re-establish the therapeutic range of your PTTs.

I know most institutions use the non-antithrombin kit, though I’m not sure whether it is an informed decision. The strength of the non-antithrombin kit is that it relies upon patient antithrombin and may reflect antithrombin deficiency, which affects heparin efficacy. I’ll do some digging with Stago, BCI, and others, and if you hear from your tech rep about this, please let me know. Geo