Anticoagulant Therapy

Xarelto Bleeding Intensity

George communicated with an acquaintance who experienced Coumadin therapy a few years ago and, subsequent to a new DVT, is now on Xarelto. He notes that minor cuts bleed longer and more profusely when on Xarelto compared to Coumadin. Can any of our subscribers confirm this?

Anticoagulant Therapy

Geometric V. Arithmetic Mean

From Dave McGlasson, does anyone have a reference on why a geometric mean is used in the INR calculation? Since we are using 20–30 normal subjects to calculate the mean PT, the range is relatively narrow. The geometric mean indicates the central tendency or typical value of a set of numbers by using the product of […]

Anticoagulant Therapy

POC and Plasma-based PT/INRs

We’ve had a number of discussions comparing point of care PT/INR results with central laboratory plasma-based PT/INRs. The December, 2017 CAP Today featured this issue in their cover article, Hemostasis, Two Hot-button Testing Issues. The first half of the article reviewed the need for age-adjusted D-dimer reference intervals for ruling out DVT and PT, and […]

Anticoagulant Therapy

When to Collect Thrombophilia Specimens

George has been communicating with Drs. Elaine Keohane (Rutgers) and Larry Smith (Abbott) about how long to wait after a thrombotic event to collect a specimen for a thrombosis risk profile. Thrombosis risk profiles include assays for antithrombin, protein C, and protein S deficiencies, which can’t be accurately measured during periods of acute inflammation (such […]

Anticoagulant Therapy

Antithrombin Deficiency Affects Heparin Assays

Another important issue addressed by Dr. James Quesenberry, St. Luke’s Laboratory, Sioux City, Iowa. His message: I understood from early on that antithrombin (AT, antithrombin III, ATIII) deficient patients can’t be assayed for unfractionated heparin using the Stago chromogenic anti-Xa heparin assay. I thought this was an all-or-none issue, only a big deal in congenital […]

Anticoagulant Therapy

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 […]

Anticoagulant Therapy

QQ for 9-17: DOAC Measurement

Here are the responses to our August, 2017 Quck Question: “How do you assay for direct oral anti-Xa antithrombotics like rivaroxaban?” A. Prothrombin time: 2 (3%) B. Partial thromboplastin time: 2 (3%) C. Chromogenic anti-Xa: 31 (48%) D. Dilute Ruessell viper venom time: 1 (2%) E. DOASENSE urine detection strip: 0 F. We don’t assay […]

Anticoagulant Therapy

DOAC Interferences

Andrew Goodwin, MD, Department of Pathology and Laboratory Medicine, University of Vermont Medical Center, told us about several substance that interfere with direct oral anticoagulant therapy and pointed us to the University of Washington Anticoagulation Services web site. For example, rivaroxaban (Xarelto) is potntiated by P-glycoprotein inhibitors and CYP3A4 inhibitors. Click or tap the link […]

Anticoagulant Therapy

Quick Question Correction

You may have noticed that our September, 2017 Quick Question contained an error: How do you assay for direct oral anti-Xa antithrombotics like dabigatran? Dabigatran, of course, is an oral direct thrombin inhibitor, not a direct anti-Xa inhibitor. This error was George’s, not Dave’s. Thanks to Dr. Emannuel Favaloro, who wrote: just advising that your […]

Anticoagulant Therapy

September QQ: DOAC Assay

Our September, 2017 Quick Question asks, How do you assay for direct oral anti-Xa antithrombotics such as rivaroxaban? The question, provided by friend and colleague, Dave McGlasson, also applies to apixaban, betrixaban, and edoxaban, all FDA-approved oral anti-Xa antithrombotics. What has never been approved is the chromogenic anti-Xa assay, despite release of calibrators and controls […]

Anticoagulant Therapy

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George Fritsma is a medical laboratory scientist, educator, and author. George holds faculty appointments with Rutgers University and Michigan State University, and is a member of the International Society on Thrombosis and Hemostasis, American Association of Clinical Chemists, and American Society for Clinical Laboratory Science.

Cheat Sheets from George

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