Monitoring Direct Thrombin Inhibitors With Calibrated Diluted Thrombin Time vs Activated Partial Thromboplastin Time in Pediatric Patients

Objectives Activated partial thromboplastin time (aPTT) is the primary test used to monitor intravenous (IV) direct thrombin inhibitors (DTIs) but has many limitations. The plasma diluted thrombin time (dTT) has shown better correlation with DTI levels than aPTT. This study compared dose-response curves for dTT and aPTT in pediatric patients receiving argatroban and bivalirudin. Methods A retrospective review of pediatric patients treated with argatroban (n = 45) or bivalirudin (n = 14) monitored with dTT and aPTT. Results The dTT assay was calibrated to report DTI concentrations in mu g/mL for argatroban and bivalirudin with good analytic sensitivity and specificity. The dTT was fivefold more likely to show a stable dose-response slope than the aPTT (P < .0002; odds ratio, 4.9). For patients in whom both dTT and aPTT showed a significant correlation between dose and assay results, dTT had a higher average correlation factor compared with aPTT (P = .007). Argatroban dose-response slopes showed more inter- and intrapatient variation than bivalirudin (dose-response slope coefficient of variation, 132% vs 52%). Conclusions The dTT assay was more likely to show a stable dose response and have a stronger correlation with DTI dose than aPTT. Argatroban shows more variation in dose response than bivalirudin.