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- Title
The international normalized ratio (INR) for monitoring warfarin therapy: reliability and relation to other monitoring methods.
- Authors
Le, D T; Weibert, R T; Sevilla, B K; Donnelly, K J; Rapaport, S I
- Abstract
<bold>Objective: </bold>To enhance understanding of the reliability of the international normalized ratio (INR) for monitoring warfarin therapy and its relation to other monitoring techniques.<bold>Design: </bold>Prospective cohort study.<bold>Setting: </bold>A university hospital.<bold>Patients: </bold>79 patients attending an anticoagulation clinic.<bold>Measurements: </bold>International normalized ratios obtained with a portable capillary monitor (Coumatrak) and the following from a simultaneous plasma sample: INRs from prothrombin times done with six thromboplastins, prothrombin-proconvertin (P&P) test activity, specific prothrombin activity, and native prothrombin antigen.<bold>Results: </bold>Converting to INRs failed to standardize prothrombin time results obtained with high- and low-sensitivity thromboplastins. Coumatrak INRs correlated best with INRs obtained with high-sensitivity thromboplastins. The INR range of 2.0 to 3.0 corresponded to a P&P range of 30% to 13%, a native plasma prothrombin antigen range of 56 to 24 micrograms/mL, and a specific prothrombin activity range of 43% to 21%.<bold>Conclusions: </bold>Low-sensitivity thromboplastins may give erroneously high INRs in the upper therapeutic range. Plasma prothrombin times should be done with a high-sensitivity thromboplastin, particularly in patients maintained at the upper limit of the therapeutic range. An INR so obtained correlated well with an INR obtained with a portable capillary blood monitor.
- Subjects
DRUG therapy; WARFARIN; ANTIGENS; BLOOD coagulation factors; CAPILLARIES; COMPARATIVE studies; DRUG monitoring; LONGITUDINAL method; RESEARCH methodology; MEDICAL cooperation; REGRESSION analysis; RESEARCH; THROMBOPLASTIN; EVALUATION research; PROTHROMBIN time
- Publication
Annals of Internal Medicine, 1994, Vol 120, Issue 7, p552
- ISSN
0003-4819
- Publication type
journal article