Here is an in-depth response from Russell Higgins, MD, a colleague of John Olson, MD, and current chair of the Coagulation Resource Committee of the College of American Pathologists (CAP) to Dee McMichael’s March 2 question about monitoring factor activity in the presence of an inhibitor:
From Dr; Olson: “We discussed this at our weekly coagulation consensus conference this morning. It reflects our thoughts on the questions. I believe that the CLSI document on assays recommends that dilution up to 1:160, but, as pointed out by Dr. Higgins, I’m not aware of data behind this recommendation. I believe that it was a consensus opinion.”
Higgins Factor Assay 3-9-13
From Dee McMichael, Blood Bank Supervisor, All Children’s Hospital, St. Petersburg, FL:
I was trying to post a question on your site but each time I received a connection failure. I will follow up with my IT department but thought I might be able to post my question in an email.
(Dee, we apologize for the connection inconvenience, which may be an issue traceable to our service provider. For anyone having difficulty logging in, please email me at george@fritsmafactor.com for follow-up, we can swiftly resolve the issue.)
Dee’s question follows:
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There is a helpful new “mdredjka” comment appended to our April 7, 2010 discussion on Fitzgerald Factor assays that was started by Peter Clement, then a student at Brigham Young University. Please take a look!
From Dave McGlasson: George, Here is a potential answer for Kelly Townsend’s February 13 post, Factor II Assay in place of INR.
Kelly is right. We did look at the chromogenic factor X and published that work a few years ago McGlasson DL, Romick BG, Rubal BL. Comparison of a chromogenic factor X assay with international normalized ratio for monitoring oral anticoagulation therapy. Blood Coagulation and Fibrinolysis 2008; 19:513–17. We found that when the INR was above 3.0, big differences occurred in correlations. The INR thusly was invalid. We had instaances when a subject had an INR of 12.8 who had almost the same level of FX as many people in the therapeutic range.
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I spoke with Patti Tichenor, UAB special coagulation laboratory who had discussed our December 5, 2012 factor VIII linearity question from Mahnaz Sairi with her UAB colleague Laura Taylor. UAB uses high-end coagulometers (Stago STA-R) for their factor assays, and their linearity extends from near zero to 100%. When they anticipate especially high factor VIII levels, they will order dilutions to as high as 1:60 (recall the initial dilution is 1:10). Using this method, they recently report a FVIII activity level of over 700% on a renal failure patient.
From Maria Franco, Orlando Health: Hi, George, when running factor assays (1:10, 1:20, etc), is the agreement between results to r/o inhibitory activity all calculated from the original result (1:10)? Not sure what the most common or recommended practice is. I have heard to find the mean of all results and then try to calculate the deviation. Thanks, Maria.
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Paul Riley, PhD, mentions Stago’s new research use only assay Asserachrom VIIa-AT that measures the activated factor VIIa-antithrombin complex (VIIa-AT, similar to the familiar thrombin-antithrombin complex), an analyte elevated in hypercoagulable states. Dr. Riley suggests the assay may be a potential surrogate biomarker for activated coagulation states. The press release and a series of references are attached here.
Stago Factor VIIa-AT Press Release
Stago VIIa-AT References
From Carol Gizzi at Baycare in Florida, We perform the factor VIII assay with a silica activated activated partial thromboplastin time (APTT, PTT) reagent. We monitor hemophilic patients. Recently we were asked to switch our reagent to a PTT reagent using ellagic acid as the activator. We do not understand the reason for the request. We thought the silica activated reagent was the most sensitive? Are we incorrect?
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Factor Assays | George Fritsma | 
March 9, 2013 11:03 am | 
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