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Anti-Xa; Do You Still Offer PTT?

From Kim Kinney, Indiana University, Hi George, one question leads to another. We have a meeting tomorrow (Tuesday, May 6) with our anticoagulation committee and one question that I think will come up will be, if we do convert to the chromogenic anti-Xa method for monitoring heparin, will we still maintain the therapeutic partial thromboplastin time (PTT, aPTT) range for those patients who must be monitored by the aPTT? For example, elevated bilirubin levels. It seems that doing this, at least from the lab’s standpoint, would not decrease lab costs or time involved in checking the PTT therapeutic range with each lot change. Sounds like that would need to be maintained. What are other institutions doing? As always, the input is appreciated.

Hi, Kim, thank you for the question. I checked with the coagulation tech specialist at our local institution that switched to the anti-Xa last year. Indeed, they continue offering the PTT for icteric and lipemic specimens and also specimens with systemic hemolysis, which often occurs with extracorporeal membrane oxygenation (ECMO). In anti-Xa testing, the specimen is diluted 1:4, not enough of a dilution to eliminate light path interference so there needs to be an alternative. Also, there are still a few surgeons who insist on the PTT. The lab does continue to do the Brill-Edwards ex vivo curve-based therapeutic range for the times a PTT becomes necessary. I’m eager to learn if other institutions are following the same policy.

Comments (2)
Anticoagulant Therapy
Jun 17, 2014 11:17am

We offer both tests and do maintain a current heparin therap
We offer both tests and do maintain a current heparin therapeutic range for our PTT-A. Luckily, our Stago PTT-A reagent has demonstrated great lot to lot stability and we have not had to change our reference range or HTR for several years.
Kelly Townsend, TriCore Reference Laboratories

May 8, 2014 8:14am

I also agree that dual monitoring of UH therapy should be av
I also agree that dual monitoring of UH therapy should be available for clinicians when the anti-Xa assay (high bilirubin, high free hemoglobin, low AT) or PTT (elevated FVIII, LA, increased PT/INR, deficiency of, FXII, PK or HMWK) fails.

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