From Ning Tang: Hi, George, I come from a clinical laboratory in China. We met a confusing case today and want to get your suggestion: A patient had a prolonged prothrombin time (PT, 20s), partial thromboplastin time (APTT, PTT, 52s) and thrombin time (TT, 127s). Fibrinogen activity is within reference interval (by both Clauss method and TEG), also the patient shows slight bleeding symptoms, is this dysfibrinogenemia? How to confirm it? Thanks for your help!
From Suakimi Pouhila, Auckland District Health Board, New Zealand. We have a patient which showed high D-dimer results with Siemens’ Innovance D-dimer but normal Stago D-dimer results. Has anyone seen this before? Is this due to cross reaction with a heterophile antibody?
Hello, Suakimi Pouhila, and thank you for your question. The various monoclonal antibodies that are employed in the D-dimer assays by manufacturers all have slightly different targets, thus there are often discrepancies among results, as illustrated by the variance in results of external quality assurance programs. However, the degree of discrepancy that you describe is unusual. I’ve contacted my US acquaintances at Siemens and Stago to learn if they have any insight.
From Michael Suter, MT (ASCP) SH Senior Clinical Scientist, Hematology, Peace Health Laboratories, Springfield, Oregon.
George, I am curious about your thoughts on how to best address the effect of high hematocrits (HCTs) on the quantitative latex D-dimer assays such as the Stago D-Di test. With high HCT samples, there is a relative decrease in plasma causing a relative excess of anticoagulant. With prothrombin time (PT) and partial thromboplastin time (PTT, APTT), it’s necessary to redraw the patient into a tube with a decreased amount of anticoagulant to normalize the plasma:anticoagulant ratio. You can’t simply correct mathematically for the excess anticoagulant, because the effect is more than dilutional and the test may end up measuring citrate anticoagulation instead of just the in vivo patient anticoagulation. Empirical studies were required to show that high HCT becomes significant above 55%.
I received an upbeat note from Dean Willett at Instrumentation Laboratory (IL) describing their ACL AcuStar specialty testing instrument, which provides an automated D-dimer immunoassay with a 30-minute dwell time, broad linearity, and a 60 specimen/h throughput.
Dean’s comment led me to reflect on the history of D-dimer methodology and to develop a quick review on what is currently available.
From friend and colleague, Kirk Guyer: How would you monitor fibrinolysis to determine when to administer tranexamic acid (Cyklokapron)? I know there are the traditional tests like serial fibrinogens, thrombin time, thromboelastograph (TEG) and reptilase time but do you know of any new tests that are becoming popular?
Question re-published from December 28, 2011 in an attempt to attract responses.
The December, 2011 issue of Clinical Laboratory News has a concise article describing the role of D-dimer in diagnosing pulmonary embolism. A lot has been written about the value of the D-dimer in ruling out venous thromboembolic disease in patients who have a low pre-test probability of a thrombus. Conversely, you see little about the use of the D-dimer for monitoring DIC. Of course, the results in DIC are extreme, often exceeding 10,000 ug/mL, but we have no limit that defines DIC nor is there any apparent value in following D-dimer results to define DIC resolution. I’d like to get some comments on this, do you routinely use D-dimer to follow DIC?
From Joanna Carroll, MT (ASCP), North Carolina State University College of Veterinary Medicine. We are running automated D-dimers and recently got a result of 0.00 ng/mL. Have you seen a value reported this low? Would it be better to report out the number as less than our lower limit of the reference range? Thanks for your help.
Thank you to all who attended George’s presentation, Case Studies in Antithrombotic Therapy, made on Friday, October 12 at the Quest Diagnostics Case-oriented Symposium on Bleeding and Thrombosis in Crystal City, VA, near Washington, DC. As promised, here is my presentation in 6-per-page handout format. Please click the link and feel free to download the file.