From Deanna Miller, Children's Hospital of Alabama. Do you have any good references for diluted thrombin and utilization of this test? What dilution is best? 1:1 or 1:3?
Hello, Deanna, and thank you for your question. We use the plasma-diluted thrombin time to measure the direct thrombin inhibitors [DTIs] dabigatran, argatroban, or bivalirudin. The assay is similar to the standard thrombin time in which human calcium thrombin reagent using approximately 5 NIH thrombin units is added to test plasma and the interval to clot formation in seconds is measured. A normal thrombin time in many laboratories is less than 21 seconds. When measuring DTIs, the test plasma is first diluted 1:10 with imidazole buffer, then one part of the dilution is added to two parts pooled normal plasma. The results in seconds are proportional to DTI concentration. I've attached the Hyphen BioMed Hemoclot™ Thrombin Inhibitors Assay package insert [click], which provides linearity data and references. Despite being linear, accurate, and reproducible, the Hyphen assay has never been FDA-approved and the US package insert is labeled for research use only.