Time in the Therapeutic Range for Assessing Anticoagulation Quality in Patients Receiving Continuous Unfractionated Heparin

Due to variable pharmacokinetic properties, therapeutic anticoagulation with continuous unfractionated heparin (UFH) requires ongoing laboratory monitoring, generally with activated partial thromboplastin time (aPTT). In the ambulatory setting, clinicians who manage warfarin therapy often use time in the therapeutic range (TTR) to estimate a percentage of time the international normalized ratio is therapeutic. We applied the TTR concept to aPTT monitoring for therapeutic UFH and used 2 methodologies for estimation: percentage of aPTT values in range (%aIR) and a modification of the Rosendaal method (mod-Rosendaal). This study included adult inpatients admitted between September 30, 2015, and September 30, 2016, at Brigham and Women’s Hospital. For each patient, all available aPTT values were extracted to calculate 2 individual TTRs according to each methodology. Comparison between methods was performed using Student t test, and correlation was assessed with simple linear regression. A total of 255 patients were included in this study. The major outcome of TTR estimation was significantly higher using mod-Rosendaal (43.7% [26.5%]) versus %aIR (37.7% [25.7%], P = .012) by a mean difference of 6% points (95% confidence interval: 1.3-10.7). Time in the therapeutic range estimated by mod-Rosendaal significantly correlated with those estimated by %aIR ( r = 0.84, P < .001). Further studies should evaluate the correlation between TTR and clinical outcomes and establish a benchmark for quality therapeutic anticoagulation with continuous UFH.