Recombinant Thromboplastins vs Tissue-Extract Thromboplastins in Patients on Unstable Oral Anticoagulant Therapy

To the Editor:In a previous report in Clinical Chemistry , we described much higher international normalized ratios (INRs)1 with recombinant Neoplastin R (Roche Diagnostics) than with tissue-extract Neoplastin Plus (Roche Diagnostics) in patients initiating oral anticoagulant therapy (1). For patients on stable oral anticoagulation, we observed no significant differences in INRs between the thromboplastins. The increased INR values with Neoplastin R during unstable anticoagulation, such as in the initial phase of oral anticoagulation treatment, could be explained by fluctuations in coagulation factor VII (FVII) concentrations owing to the low half-life of FVII. Recombinant thromboplastin exhibits an increased sensitivity for FVII compared with tissue-derived thromboplastin (2, 3). The difference in sensitivity between Neoplastin R and Neoplastin Plus for FVII could implicate alterations in anticoagulation dosage and time period in obtaining stable anticoagulation. We investigated whether our findings could be extrapolated to other recombinant thromboplastins.We collected and citrate-treated blood samples from 20 patients in the initial phase of …