A provocative message from Dr. Michael Blechner at University of Kentucky:
This is a question about LMWH assays. We have been using Stago calibrators to generate our LMWH curve for our anti-Xa assay. We run on two Siemens BCS XPs. Siemens has recently made their own calibrator available and we have been comparing the two. On head to head comparisons of real patients, the Siemens results are biased upwards by 0.23 units on average (60 specimens). We also threw the latest CAP survey at both calibrator sets.
The results were as follows:
We also tested the Siemens calibrators and controls using the Stago generated curve and vice versa …
Siemens uses a single calibrator which is automatically diluted on the instrument.
Has anyone else out there made this switch and seen similar results? Which one is correct? Any suggestions? Thanks again.
Michael D. Blechner, M.D.
Assistant Professor, Pathology & Laboratory Medicine
Director, Pathology Informatics
Director, Coagulation Laboratory
University of Kentucky Medical Center
Hi, Dr. Blechner, good to hear from you again. I forwarded your question to Dave McGlasson, MS MT (ASCP), coagulation research specialist at the Wilford Hall USAF Hospital in San Antonio, and as you know, he phoned you on Friday, 7/16/2010 to review your data. Dave has done a great deal of research on LMWH monitoring, so I sent him your data and discussed it with him on Friday prior to his call to you. Dave and I agreed there is a discrepancy, and I’m certain this post will attract attention from both Stago and Siemens.
Dave, however, went past the issue to describe application of the hybrid curve, about which he has two publications, both attached to this post below. Dave claims, and his approach has now been verified at several institutions, that one curve can be used to measure both unfractionated and low molecular weight heparin, eliminating the need for switching between curves. I hope this is helpful, and meanwhile I invite Siemens and Stago contact us to help resolve the systematic discrepancy you describe above.
Here are Dave’s two publications:
- McGlasson DL. Using a single calibration curve with the anti-Xa chromogenic assay for monitoring heparin anticoagulation. Lab Med 2005;36:1-3.
- McGlasson DL, Kaczor DA, Krasuski RA, et al. Effects of pre-analytical variables on the anti-activated factor X chromogenic assay when monitoring unfractionated heparin and low molecular weight heparin anticoagulation. Blood Coagul Fibrinolysis 2005;16: 173-176.