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Anti-Xa and PTT Conflict

George met James T. Quesenberry, MD, FCAP, Medical Director, St. Luke’s Laboratory, UnityPoint Health at the Mayo Medical Laboratories Bleeding and Thrombosing Diseases conference, Rochester, MN, September 13–15, 2017. Dr. Quesenberry subsequently addressed the issue of the ant- Xa vs PTT in monitoring heparin therapy. His message, “Our protocol for unfractionated heparin dosing uses the anti-Xa as the standard lab measurement for dose adjustments. We use Stago instrumentation with a hybrid curve. To my knowledge this has worked out well generally. We have had occasional patients, older patients with prior normal PT/PTTs who are therapeutic as far as anti-Xa level goes but then someone orders a PTT and they are high. In today’s instance both the Xa and PTT were redrawn and they do repeat. Our QC and proficiencies with the Stagos are fine reportedly. Any advice?  Thank you.”

George passed Dr. Quesenberry’s question along to Lawrence “Lance” Williams, MD, Medical Director of the special coagulation laboratory at University of Alabama at Birmingham, who has grappled with this problem previously. Here is Dr. Williams’ reply:

“James, As you may know, this is not all that uncommon. If you had more random testing of both assays, you would see more of this than you would ever want to deal with. The question is, when is it clinically significant? And that is an unanswered question as of now. At our hospital, when we see this, we only act on the high PTT if the patient is bleeding or at very high risk of bleeding. In those instances, we titrate based on the PTT. This is the more conservative approach because the patient may have an underlying coagulopathy that is being reflected by the PTT, but is not necessarily due to the heparin therapy. Lance”

As this is a common and serious issue, I invite our participants to comment on their approach. Thanks to Drs.Quesenberry and Williams for their expertise.

Oct 10: George has added a link to Dr. Zehnder’s presentation that was referenced by Dr. Vadim Kostousov in the attached comment. Tap or click the link here to see Dr. Zehnder’s presentation:

Comments (1)
Anticoagulant Therapy
Oct 9, 2017 5:30pm

Excellent slide presentation
An excellent slide presentation from Dr. James Zehnder is available on the ISLH web site:
Beginning from slide #21: besides commonly known factors such as coagulopathy or transient lupus anticoagulant, mild (transient? cancer-related?) factor XII deficiency and elevated CRP could contribute to the elevated APTT when anti-Xa activity remains within the target range.
Note from George: Thanks to Dr. Kostousov for this reference, the entire presentation helps solve the problem of discordant anti-Xa and PTT results for people receiving unfractionated heparin.

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