title: Potential dosing errors using portable prothrombin time monitoring devices.
abstract: Portable prothrombin time (PT) monitors facilitate the control of warfarin therapy. Few studies have compared the influence of using different monitors on dosage decisions. We determined the comparability of data generated by two portable PT monitors, Coaguchek S, (Roche Diagnostics Boehringer-Mannheim) and Hemochron Jr (International Technidyne Corporation Ltd.), with that of a reference laboratory. Simultaneous International Normalized Ratio (INR) measurements (portable monitor and laboratory) were performed in 193 consecutive patients receiving warfarin for at least 3 months. Agreement of measurements was assessed by both regression analysis and influence on dosage decisions in accordance with pre-defined criteria. The Coaguchek S versus laboratory INR regression line (n = 111; r2 = 0.88; P < 0.001) was close to the line of identity, while that of the Hemochron Jr (n = 82; r2 = 0.61; P < 0.001) was not. The overall proportion of dual INR measurements that fulfilled the clinical criteria of agreement was 90% for the Coaguchek S compared with 62% for the Hemochron Jr (P < 0.0001). For laboratory INRs 2.0-2.5, 2.6-4.0 and > 4.0, the proportions of portable measurements that satisfied the clinical criteria for the Coaguchek S versus the Hemochron Jr were 96 versus 63% (P < 0.001), 81 versus 45% (P < 0.04), and 67 versus 17% (P < 0.85), respectively. Warfarin dosing based solely on the portable devices would have resulted in unjustified dose increments in 22% of the patients with the Hemochron Jr device compared with 8% with the Coaguchek S monitor (chi2 = 4.43; P = 0.035). The Coaguchek S monitor provides measurements for INR values within the therapeutic range that agree well with the standard laboratory. The Hemochron Jr measurements result in different dosage adjustments even within the therapeutic range, but especially for INR values > 4.0. For both monitors, agreement of INR measurements with the standard decreases with increasing INR values.
authors.affiliation: Institute of Clinical Pharmacology and Toxicology, The Chaim Sheba Medical Center, Tel Hashomer, Israel.
authors.forename: Ronen
authors.initials: R
authors.lastname: Loebstein
authors.forename: Daniel
authors.initials: D
authors.lastname: Kurnik
authors.forename: Aharon
authors.initials: A
authors.lastname: Lubetsky
authors.forename: David
authors.initials: D
authors.lastname: Ezra
authors.forename: Hillel
authors.initials: H
authors.lastname: Halkin
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000925:Anticoagulants / Q000008:administration & dosage* / Q000494:pharmacology; D001777:Blood Coagulation / Q000187:drug effects; D005260:Female; D006801:Humans; D019934:International Normalized Ratio; D008297:Male; D008508:Medication Errors / Q000517:prevention & control; D008875:Middle Aged; D011517:Prothrombin Time / Q000295:instrumentation* / Q000592:standards; D012016:Reference Values; D015203:Reproducibility of Results; D014859:Warfarin / Q000008:administration & dosage* / Q000494:pharmacology
chemical_list: D000925:Anticoagulants; D014859:Warfarin