Standardization and harmonization of coagulation testing methods have come a long way in the last 3 to 4 decades; however, standardization is imperfect. Laboratory professionals need to recognize the limitations of some of our most commonly used coagulation tests. The INR system has harmonized prothrombin time across methods and platforms for the purpose of monitoring warfarin, but the system does not harmonize very high INR values nor does it harmonize INR values in the setting of liver disease. Many hospital-based laboratories perform a one stage factor VIII assay to support a wide range of clinical indications. In the last decade, important biases have been demonstrated between one stage assays and chromogenic assays when diagnosing hemophilia A patients or monitoring new hemophilia therapies. Finally, quantitative D-dimer assays have excellent negative predictive value to exclude venous thromboembolism. Unfortunately, there is a lack of standardization, and even a lack of a standardized unit of measure. Implementation of D-dimer requires careful attention to both the unit of magnitude and the unit type, especially when using different instrumentation across a laboratory system.
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