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Factor XII Deficiency and Thrombosis

Janice Richardson asks, “Why does a low factor XII cause clotting?” Factor XII was described in 1955 by Ratnoff and Colopy who recognized its deficiency in an American male, John Hageman. Factor XII deficiency causes a markedly prolonged activated partial thromboplastin time (APTT, PTT) but paradoxically does not associate with bleeding. Most of us know […]

Lupus Anticoagulant Targets Factor XI

From Eric Creager at Diagnostica Stago: I am curious why a strong lupus anticoagulant seems to target factor XI?. I have seen multiple cases of strong LA with a FXI assay as low as 10%. Serial dilutions sometimes show increasing FXI activity results with larger dilutions. Most recent case was a 44 YO male appearing […]

Case Study: Coumadin Dosage

I monitor the ASCLS Consumer Forum regularly for hemostasis-related questions from patients and health care providers. The forum receives an average of 50 questions a day, typically five that have to do with coagulation. I’m amazed at how active the forum is, and at the energy and expertise of the ASCLS volunteers who answer questions. One thing […]

Prothrombin Time Delta Check

Here are the results of our March 18, 2009 quick question: What do you use as a delta-check method for the prothrombin time test? a. INR: 17 (34%) b, PT in seconds: 7 (14%) c. Combination of INR and seconds: 13 (26%) d. No delta-check: 13 (26%) This is a relatively even distribution. Let’s next […]

Bridging with Antithrombotics During Orthopedic Surgery

Here is a surgery question from Dan Southern, friend and retired professor from Western Carolina University’s Clinical Laboratory Science program: After meeting with my surgeon, I started in motion something that I want your opinion on.He told me that I would be on Coumadin prior and six weeks after hip replacement surgery Based on experience, […]

New Oral Anti-Xa Anticoagulant?

I received a message from Eric Hardy, a 1990s graduate of our University of Alabama at Birmingham CLS program and now a physician assistant practicing in the area. A McNeil Labs representative was advocating for one of the new oral anti-Xa anticoagulants . I have seen no announcement nor ads indicating any of the new […]

Factor VIII Inhibitor Assay

A question from Bruce King at Lancaster General: I was wondering about the practicality of adding a test for factor VIII inhibitors in our community hospital setting. Although we don’t get many requests for it, it appears that when you get a request for a factor VIII inhibitor in a non-hemophilia patient, there is a […]

Pharmacogenetic Warfarin Dose Estimation

The most recent large validation cohort study that supports screening for CYP2C9 and VKORC1 polymorphisms to assist in estimating warfarin dosage is available at The International Warfarin Pharmacogenetics Consortion: Estimation of the warfarin dose with clinical and phamacogenetic data. NEJM 2009; 360: 753-764. Geo

Delta Checks

Please respond to the quick question posted 2-19-09 on prothrombin time delta checks. Our question system does not provide for an open-ended response, but in addition to choosing the reporting format, we would like to compute the average delta check range. Please report your range as a response to this posting, thank you. Geo

Cold Agglutinins and Clotting

Another good one from Kim Kinney at Clarian: Hi George, I have a question regarding cold agglutinins and clotting coag samples. I have heard from one of our sites that specimens from someone with a cold agglutinin will clot in citrate tubes. In order to get a good sample the tubes and the blood must […]

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George Fritsma is a medical laboratory scientist, educator, and author. George is a member of the International Society on Thrombosis and Hemostasis, the International Society for Laboratory Hematology, and the American Society for Clinical Laboratory Science.

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